Frames

Typographical glossary

- A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z -

A
Advance Width
The distance between the start of this character and the start of the next character. Sometimes called the character's width.
Ascender
A stem on a lower case letter which extends above the x-height. "l" has an ascender.
See also X-height, Cap-height, Descender, Overshoot, Baseline
Anchor Class
Used to specify mark-to-base and cursive GPOS subtables. See overview.
Ascent
In traditional typography the ascent of a font was the distance from the top of a block of type to the baseline.

Its precise meaning in modern typograph seems to vary with different definers.

ATSUI
Apple's advanced typographical system
B
Baseline
The baseline is the horizontal line on which the (latin, greek, cyrillic) letters sit. The baseline will probably be in a different place for different scripts. In Indic scripts most letters descend below the baseline. In CJK scripts there is also a vertical baseline usually in the middle of the character.
See also X-height, Cap-height, Ascender, Descender, Overshoot
Bézier curve or Bézier splines
Bézier curves are described in detail in the Bézier section of the main manual.
Black letter
Any of various type families based on medieval handwriting.
See also gothic.
BMP (Basic Multilingual Plane)
The first 65536 code points of Unicode. These contain most of the ordinary characters in the world.
Bold
A common font style. The stems of the characters are wider than in the normal font, given the letters a darker impression.
Boustrophedon
Writing "as the ox plows", that is alternating between left to right and right to left. Early alphabets (Old Canaanite, and the very early greek writings (and, surprisingly, fuþark)) used this. Often the right to left glyphs would be mirrors of the left to right ones.
C
Cap-height
The height of a capital letter above the baseline (with a flat top like "I" as opposed to one with a curved to like "O").
See also X-height, Ascender, Descender, Overshoot, Baseline
CFF
Compact Font Format used within OpenType postscript fonts.
Character
A character is a Platonic ideal reified into at least one glyph. For example the letter "s" is a character which is reified into several different glyphs: "S", "s", "s", long-s, etc. Note that these glyphs can look fairly different from each other, however although the glyph for an integral sign might be the same as the long-s glyph, these are in fact different characters.
Character set
A character set is an unordered set of characters
CID
In some CJK PostScript fonts the glyphs are not named but are refered to by a CID number.
CID-keyed font
A PostScript font in which the glyphs
CJK
Chinese, Japanese, Korean. These three languages require fonts with a huge number of characters. All three share a writing system based on Chinese ideographs (though they have undergone seperate evolution in each country, indeed mainland Chinese fonts are different from those used in Taiwan and Hong Kong).

Japanese and Korean also have phonetic syllabaries. The Japanese have two syllabaries, hiragona and katakana which have about 60 syllables. The Koreans have one syllabary, hangul with tens of thousands of syllables.

CJKV
Chinese, Japanese, Korean, Vietnamese. These four languages require fonts with a huge number of characters.
Condensed
A condensed font is one where the space between the stems of the characters, and the distance between characters themselves has been reduced.
D
Descender
A stem on a lower case letter which extends below the baseline. "p" has a descender.
See also X-height, Cap-height, Ascender, Overshoot, Baseline
Descent
In traditional typography the descent of a font was the distance from the bottom of a block of type to the baseline.

Its precise meaning in modern typograph seems to vary with different definers.

Didot point
The European point. 62 2/3 points per 23.566mm ( 2.66pt/mm or 67.54pt/inch )
E
em
A linear unit equal to the point size of the font. In a 10 point font, the em will be 10 points. An em-space is white-space that is as wide as the point size. An em-dash is a horizontal bar that is as wide as the point size.

An em-square is a square one em to each side. In traditional typograph (when each letter was cast in metal) the glyph had to be drawn within the em-square.

em unit
In a scalable font the "em" is subdivided into units. In a postscript font there are usually 1000 units to the em. In a TrueType font there might be 512, 1024 or 2048 units to the em. In an Ikarus font there are 15,000 units. PfaEdit uses these units as the basis of its coordinate system.
en
One half of an "em"
Encoding
An encoding is a mapping from a set of bytes onto a character set. It is what determines which byte sequence represents which character. The words "encoding" and "character set" are often used synonymously. The specification for ASCII specifies both a character set and an encoding. But CJK character sets often have multiple encodings for the character set (end multiple character sets for some encodings).

In more complicated cases it is possible to have multiple glyphs associated with each character (as in arabic where most characters have at least 4 different glyphs) and the client program must pick the appropriate glyph for the character in the current context.

Even-Odd Fill rule
To determine if a pixel should be filled using this rule, draw a line from the pixel to infinity (in any direction) then count the number of times contours cross this line. If that number is odd then fill the point, if it is even then do not fill the point. This method is used by postscript rasterizers after level 2.0 of PostScript. See Also Non-Zero Winding Number Fill.
Extended
An extended font is one where the space between the stems of the characters, and the distance between characters themselves has been increased.
F
Font
A collection of glyphs, generally with at least one glyph associated with each character in the font's character set, often with an encoding.

A font contains much of the information needed to turn a sequence of bytes into a set of pictures representing the characters specified by those bytes.

In traditional typesetting a font was a collection of little blocks of metal each with a graven image of a letter on it. Traditionally there was a different font for each point-size.

Font Family, or just Family
A collection of related fonts. Often including plain, italic and bold styles.
FreeType
A library for rasterizing fonts. Used extensively in PfaEdit to understand the behavior of truetype fonts.
Fractur
The old black letter writing style used in Germany up until the end of world war II.
See also gothic.
G
Glyph
A glyph is an image, often asociated with one or several characters. So the glyph used to draw "f" is associated with the character f, while the glyph for the "fi" ligature is associated with both f and i. In simple latin fonts the association is often one to one (there is exactly one glyph for each character), while in more complex fonts or scripts there may be several glyphs per character (In renaissance printing the letter "s" had two glyphs associated with it, one, the long-s, was used initially and medially, the other, the short-s, was used only at the end of words). And in the ligatures one glyph is associated with two or more characters.

Fonts are collections of glyphs with some form of mapping from character to glyph.

Grid Fitting
Before TrueType glyphs are rasterized they go through a process called grid fitting where a tiny program (associated with each glyph) is run which moves the points on the glyph's outlines around until they fit the pixel grid better.
Gothic
The German monks at the time of Gutenburg used a black-letter writing style, and he copied their handwriting in his typefaces for printing. Italian type designers (after printing spread south) sneered at the style, prefering the type designs left by the romans. As a term of contempt they used the word gothic, the style of the goths who helped destroy the roman empire.
Grotesque
See also sans-serif.
H
Hints
These are described in detail in the main manual. They help the rasterizer to draw a glyph well at small pointsizes.
I
Italic
A slanted style of a font, generally used for emphasis.

Italic differs from Oblique in that the transformation from the plain to the slanted form involves more than just skewing the letterforms. Generally the lower-case a changes to a, the serifs on lower-case letters like i (i) change, and the font generally gains a freer look to it.

J
K
Kerning
When the default spacing between two characters is inapproriate the font may include extra information to indicate that when a given character (say "T") is followed by another character (say "o") then the advance width of the "T" should be adjusted by a certain amount to make for a more pleasing display.
Kern pair
A pair of characters for which kerning information has been specified.
L
Left side bearing
The horizontal distance from a character's origin to its leftmost extent. This may be negative or positive.
Lemur
A monotypic genus of prosimian primates, now found only on Madagascar but formally (about 50 million years ago) members of this family were much more wide spread.
Ligature
A single glyph which is composed of two adjacent characters. A common example in the latin script is the "fi" ligature which has a nicer feel to it than the sequence.
LGC
Latin, Greek, Cyrillic. These three alphabets have evolved side by side over the last few thousand years. The letter forms are very similar (and some letters are shared). Many concepts such as "lower case", "italic" are applicable to these three alphabets and not to any others.
M
Monospace
A font in which all characters have the same advance width. These are sometimes called typewriter fonts.
Multiple Master Font
A multiple master font is a PostScript font schema which defines an infinite number of related fonts. Multiple master fonts can vary along several axes, for example you might have a multiple master which defined both different weights and different widths of a font family, it could be used to generate: Normal, Semi-Bold, Bold, Condensed, Expanded, Bold-Condensed, etc.

PfaEdit does not currently support multiple master fonts (and Adobe is no longer developing them either).

N
Non-Zero Winding Number Fill rule
To determine if a pixel should be filled using this rule draw a line from here to infinity (in any direction) and count the number of times contours cross this line. If the contour crosses the line in a clockwise direction add 1, of the contour crosses in a counter clockwise direction subtract one. If the result is non-zero then fill the pixel. If it is zero leave it blank. This method is used by truetype and older (before version 2) postscript rasterizers.
See Also Even-Odd Fill Rule
O
OpenType
A type of font. It is an attempt to merge postscript and truetype fonts into one specification.

An opentype font may contain either a truetype or a postscript font inside it.

It contains many of the same data tables for information like encodings that were present in truetype fonts. It also can contain additional information such as positional glyph selection (needed for arabic), ligatures, etc.

OpenType Tables
Each opentype font contains a collection of tables each of which contains a certain kind of information. See here for the tables used by PfaEdit.
Oblique
A slanted style of a font, generally used for emphasis.

Oblique differs from Italic in that the transformation from the plain to the slanted form involves just skewing the letterforms.

Overshoot    
In order for the curved shape of the "O" to appear to be the same height as the flat top of the "I" it tends to "overshoot" the cap-height (or x-height, or undershoot the baseline) by about 3% of the cap-height (or x-height). For a triangular shape (such as "A") the overshoot is even greater, perhaps 5%.
These guidelines are based on the way the eye works and the optical illusions it generates and are taken from Peter Karow's Digital Formats for Typefaces, p. 26).
See also X-height, Cap-height, Ascender, Descender, Baseline
P
Panose
A system for describing fonts. See AGFA's PANOSE classification metrics guide and MicroSoft's PANOSE classification in Windows.
Pica point
The Anglo-American point. With 72.27 points per inch ( 2.85pt /mm ).
Point
A point is a unit of measurement. There were two different definitions for "point" in common usage before the advent of computers. The one in use in the Anglo-Saxon printing world was the "pica point" with 72.27 points per inch ( 2.85pt /mm ), while the one used in Europe was the didot point with 62 2/3 points per 23.566mm ( 2.66pt/mm or 67.54pt/inch ).

These two points were so arranged that text at a given point-size would have approximately the same cap-height in both systems, the didot point would have extra white-space above the capitals to contain the accents present in most non-English Latin based scripts.

This has the interesting side effect that a font designed for European usage should have a smaller proportion of the vertical em given over to the text body. I believe that computer fonts tend to ignore this, so presumably european printers now set with more leading.

As far as I can tell, computers tend to work in pica points (but this may be because I am in the US).

Point Size
In traditional typography a 10pt font was one where the block of metal for each character was 10 points high.
PostScript
PostScript is a page-layout language used by many printers. The language contains the specifications of several different font formats. The main manual has a section describing how PostScript differs from TrueType.
  • Type 1 -- This is the old standard for PostScript fonts. Such a font generally has the extension .pfb (or .pfa). A type 1 font is limitted to a one byte encoding (ie. only 256 characters may be encoded).
  • Type 2 -- This is the format used within OpenType fonts. It is almost the same as Type 1, but has a few extensions and a more compact format.
  • Type 3 -- This format allows full postscript within the font, but it means that no hints are allowed, so these fonts will not look as nice at small point-sizes. Also most rasterizers are incapable of dealing with them. A type 0 font is limitted to a one byte encoding (ie. only 256 characters may be encoded).
  • Type 0 -- This format is used for collecting many sub-fonts (of Type 1 or Type 3) into one big font, and was used for CJK or Unicode fonts.
  • Type 42 -- A TrueType font wrapped up in PostScript. Sort of the opposite from OpenType.
  • CID -- This format is used for CJK fonts with large numbers of glyphs.
Q
R
Reference
A reference is a way of storing the outlines of one glyph in another (for example in accented characters).
Right side bearing
The horizontal distance from a character's rightmost extent to the character's advance width. This may be positive or negative.
S
Sans Serif
See the section on serifs.
Script
A script is a character set and associated rules for putting letters together. Latin, arabic, katakana and hanja are all scripts.
Serif
latin
greek
cyrillic
a serif sans serif
hebrew
bet serif sans serif
Back two thousand years ago when the Romans were carving their letters on stone monuments, they discovered that they could reduce the chance of the stone cracking by adding fine lines at the terminations of the main stems of a character.

These fine lines were called serifs, and came to have an esthetic appeal of their own. Early type designers added them to their fonts for esthetic rather than functional reasons.

At the end of the nineteenth and beginning of the twentieth, type-designers started designing fonts without serifs. These were initialially called grotesques because their form appeared so strange, they are now generally called sans-serif.

Other writing systems (Hebrew for one) have their own serifs. Hebrew serifs are rather different from latin (cyrillic, greek) serifs and I don't know their history. Hebrew serifs only occur at the top of a character

I would welcome examples from other scripts of serifed and sans-serifed characters.

Spline
A curved line segment. See the section in the manual on splines. The splines used in PfaEdit are all third order Bézier splines.
Style
There are various conventional varients of a font. In probably any writing system the thickness of the stems of the characters may be varied, this is called the weight of a font. Common weights are normal and bold.

In LGC alphabets an italic (or oblique) style has arisen and is used for emphasis.

Fonts are often compressed into a condensed style, or expanded out into an extended style.

Various other styles are in occasional use: underline, overstrike, outline, shadow.

Syllabary
A syllabary is a phonetic writing system like an alphabet. Unlike an alphabet the sound-unit which is written is a syllable rather than a letter. In Japanese KataKana the sound "ka" is represented by one glyph. Syllabaries tend to be bigger than alphabets (KataKana requires about 60 different characters, while the Korean Hangul requires tens of thousands).
T
True Type
A type of font invented by Apple and shared with MicroSoft. It specifies outlines with 2 degree Bézier curves, contains inovative hinting controls, and an expandable series of tables for containing whatever additional information is deemed imported to the font.

Apple and Adobe/MicroSoft have expanded these tables in different ways, although attempting to achieve the same effect.

TrueType Tables
Each truetype font contains a collection of tables each of which contains a certain kind of information. See here for the tables used by PfaEdit.
Type 1
A type of PostScript font which see.
Type 2
A type of PostScript font, used within OpenType font wrappers.
Type 3
A very general type of PostScript font, which see.
Type 0
A type of PostScript font, which see.
Typewriter
See Monospace.
U
Unicode
An encoding character set/encoding which tries to contain all the characters used in the world. See the Unicode consortium.
More info.
V
W
Weight
The weight of a font is how thick (dark) the stems of the characters are. Traditionally weight is named, but recently numbers have been applied to weights.
Thin 100
Extra-Light 200
Light 300
Normal 400
Medium 500
Demi-Bold 600
Bold 700
Heavy 800
Black 900
Nord
Ultra
Width
This is a slightly ambiguous term and is sometimes used to mean the advance width (the distance from the start of this character to the start of the next character), and sometimes used to mean the distance from the left side bearing to the right side bearing.
X
X-height
The height of a lower case letter above the base line (with a flat top like "x" or "z" or "v" as opposed to one with a curved top like "o" or one with an ascender like "l") .
See also Cap-height, Ascender, Descender, Overshoot, Baseline
Y
Z

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