In traditional typography, a font is a particular size, weight and style of a typeface. Each font was a matched set of metal type, one piece (called a “sort”) for each glyph, and a typeface comprised a range of fonts that shared an overall design.
In modern usage, with the advent of digital typography, “font” is frequently synonymous with “typeface”. In particular, the use of “vector” or “outline” fonts means that different sizes of a typeface can be dynamically generated from one design.
The word font derives from Middle French fonte and the term refers to the process of casting metal type at a type foundry.