The two terms are different. A typeface comprises as set of characters that share certain design features such as x-height, serif shape, stress, and contrast in stroke weights. Helvetica Medium, Helvetica Black and Helvetica Bold Oblique, for example, are typefaces. (Typefaces in turn belong to type families. Those three faces belong, reasonably enough, to the Helvetica family.) When you look at a sentence printed in a book or magazine, or displayed onscreen, you are seeing text in a particular typeface.

A font is used to generate the type of a particular typeface in a particular size: for example, in 18-point Helvetica Medium or 10-point Futura. (Many people define a font as a particular size, or cut, of a typeface.) In the early days of typesetting, a font was a collection of small metal blocks separately designed and cut from a master, and the characters underwent subtle changes from one size to another. Later, a font was a filmstrip that was used like a light stencil to expose images of characters onto photographic film. Now fonts are chunks of computer code.

The terms font and typeface are frequently used interchangeably, especially today, because software programs can generate a great many enlargements and reductions of characters from a single master, or cut.