METAFONT is a font-design system created by Donald Knuth as the companion to TeX. Where TeX arranges type on a page, METAFONT defines the shapes of the type itself. It is both a programming language for describing letterforms and the program that interprets that language, turning the descriptions into the font data and bitmaps that TeX needs to render text at a given size and resolution.
The defining idea of METAFONT is parametric, programmatic type. A letter is not stored as a fixed picture but written as a small program: the designer specifies key points, the curves that connect them, and the shape and angle of an imaginary pen that traces the strokes. Because these descriptions are driven by numerical parameters, a single source can generate a whole family of related fonts. Adjusting parameters for pen width, slant, x-height, or overall darkness produces bold, italic, or differently proportioned variants from the same underlying definitions, all kept consistent by the shared mathematics.
Knuth created METAFONT because his work on TeX had no satisfactory fonts to typeset with. He needed letterforms that would reproduce identically across the wide range of output devices and resolutions of the late 1970s and 1980s, from low-resolution screens and dot-matrix printers to high-resolution phototypesetters. By describing characters mathematically rather than hand-drawing bitmaps for every size, METAFONT could digitize the same design correctly at any resolution, a problem Knuth continued to refine, noting on his Stanford pages a “new and improved procedure for digitizing the letterforms at low resolutions.”
The system is documented in Knuth’s The METAFONTbook (1986), described on his Stanford pages as “the definitive user manual and reference manual for METAFONT” and published as Volume C of the Computers and Typesetting series. Volume D, METAFONT: The Program, contains the complete annotated source in Knuth’s literate programming style, and Volume E, Computer Modern Typefaces, gives precise METAFONT definitions for about 500 letters, numerals, and other symbols.
METAFONT’s chief practical product was the Computer Modern family, the default typefaces of TeX. Although outline-font technologies such as PostScript Type 1 and later OpenType came to dominate commercial type, METAFONT’s vision of fonts as parameterized programs remained influential, and the original Computer Modern designs were eventually converted into those modern outline formats for everyday use.