The Lingua Franca of LaTeX

The typesetter that understands these commands is the TeX engine itself, which reads the author’s manuscript and produces a file that can be sent directly to a printer to produce typeset documents. Because TeX’s plain set of commands is fairly low-level, its best suited for authors who, like Knuth, desire detailed control over the typesetting of their material. Because the TeX typesetting engine was developed before digital formats for typefaces had been standardized, Knuth had to invent his own format for font files; design a set of font families, Computer Modern; and invent his own typeface design program, Metafont.

Source: increment.com