TeX font metric

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TeX font metric (TFM) is a font file format used by the TeX typesetting system. It is a font metric format, not an outline font format like TrueType, because it provides only the information necessary to typeset the font such as each character's width, height and depth. The actual glyphs are stored elsewhere. This is not unique to TeX; Adobe's AFM files and Windows' PFM (NTF on modern Windows PostScript driver) files use the same technique.

TFM files contain all of the information TeX needs to produce its device-independent (DVI) output. The actual glyphs are then inserted by the eventual DVI output driver or previewer, using, for instance, TrueType fonts, or fonts in the bitmap PK format derived from a METAFONT source. The format is designed to be extremely compact: in the original Computer Modern distribution, every font's TFM file is smaller than 2 kB.^[1]