In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of various fonts that share an overall design.
In modern usage, with the advent of computer fonts, the term "font" has come to be used as a synonym for "typeface", although a typical typeface (or "font family") consists of several fonts. For instance, the typeface "Bauer Bodoni" (sample shown here) includes fonts "Roman" (or "Regular"), "Bold" and "Italic"; each of these exists in a variety of sizes. The term "font" is correctly applied to any one of these alone but may be seen used loosely to refer to the whole typeface. When used in computers, each style is in a separate digital "font file".
In both traditional typesetting and modern usage, the word "font" refers to the delivery mechanism of the typeface. In traditional typesetting, the font would be made from metal or wood type: to compose a page may require multiple fonts or even multiple typefaces.