Type Glossary

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An em is a typographic unit of measurement equal to the computed font-size of an element (W3C). The term comes from metal type, when the width of a “one em” space referred to the width of a font’s capital letter M.
Similar to em units, a rem is a typographic unit of measurement equal to the computed value of font-size on the root element of an HTML document (W3C). Because rem units always refer to this root element, their values don’t compound like em unit values do.
An ex is a typographic unit of measurement equal the x-height of the font (the height of its lowercase x glyph). This is currently roughly calculated and doesn’t fit the true calculated x-height perfectly.
A ch is a typographic unit of measurement equal to a font’s advanced width. The glyph used for this measurement is ‘0’, or U+0030 in Unicode.
vw (viewport width) is a CSS unit of measurement equal to 1/100th of the viewport width.
vh (viewport height) is a CSS unit of measurement equal to 1/100th of the viewport height.
vmin is a CSS unit of measurement equal to 1/100th of the smallest side of the viewport.
vmax is a CSS unit of measurement equal to 1/100th of the largest side of the viewport.
A single word or short line at the end or beginning of a column isolated from the rest of its paragraph.
A single word or short line at the end of a paragraph that leaves and access amount of whitespace between its line and the adjacent paragraph.
type rendering
The translation of vector font outlines into bitmapped shapes in a given environment. Type rendering comprises many layers of technology.
The process of smoothing the edges of shapes (including typographic glyphs) by making some pixels gray instead of black or white. Sub-pixel antialiasing uses color to harness the individual red, green, and blue components of screen pixels, which often results in more accurate anti-aliasing. See also: type rendering.
The process of defining a system of rules, or instructions, for bending the vector shapes of type to fit a bitmap grid. See also: type rendering.
font formats
The file format used for storing information about a font, including its character set and metrics. Some popular font formats include OTF and TTF. For the sake of compatibility and efficiency, fonts are sometimes wrapped in additional file formats like WOFF2.
A font format based on the TrueType format. Opentype had an emphasis on international writing systems.
UFO (Unified Font Object) is a font format aiming to be cross-platform for the exchange and storing of font data.
variable fonts
Fonts that can comprise many weights, widths, and other styles of a typeface within a single file. Introduced as part of OpenType 1.8. For further reading see Variable fonts for Responsive Design and Live Font Interpolation on the Web.
A method for finding any amount of instances between two values. Interpolation can be used to generate additional font weights with a set of masters.
Flexible type considered for responsive environments.
modular scales
A method of defining a scale based off of proportional relationships. These don't have to be linear – for example, a ¾ ratio of 1em would be 1em, 1.333em, 1.777em, 2.369em, etc.
CSS Calc()
CSS units using mathematical expressions.
The measure between the baseline and the height of the lowercase letters in Latin alphabets. Other languages use different measures.
The vertical space between individual lines of type, also known as leading which originated from placing strips of lead between lines in hand-typesetting.
The local fonts that are loaded if custom fonts are blocked, or unavailable.
Local fonts
Local fonts are fonts that exist on someone’s computer. Different people have different local fonts. Local fonts can be summoned with CSS for use on websites, but we can’t expect every visitor to see the same thing. See also: fallback fonts, web fonts.
Javascript driven storage on the client side.
The CSS declaration for declaring a custom font.
optical size
Adjustments made to account for how people percieve things at different distances differently. There are a variety of approaches.
Two or more letters/graphemes joined into a single glyph. Ligatures either stylistic or represent their own letter. For example, ‘st’ and ‘ß’ respectively.