Typography has a long and varied history. Over the years, some typographic terms have lost their original meaning and have come to mean different things to different people, depending on the context. The Typekit API aims to be consistent in it's terminology, at the cost of occasionally choosing terms that might not be strictly correct.
In particular, we try to avoid the term “font” because it has become ambiguous. Traditionally a font is a complete set of glyphs, of a particular style, of a particular typeface, at a particular size. Presently the term can be used to represent anything from a type family (FacitWeb) to a particular weight and style of that family (FacitWeb Extra Light Italic) to the files that constitute the typeface as software.
The terms Typekit's API uses include:
Font Family
A “Font Family” (or simply, “Family”) is a collection of “Font Variations” that share a common visual style. Examples include FF Meta Web Pro, Droid Sans, and Coquette. Traditionally, this has also been called a type family.
Font Variation
A “Font Variation” (or simply, “Variation”) is a particular weight and style of a “Font Family”. Examples include FF Meta Web Pro Bold Italic, Droid Sans Regular, and Coquette Light. Traditionally, this might be referred to as a style or type style.
Typekit uses Font Variation Descriptions to concisely and unambiguously refer to font variations in the API.
Subset
A “Subset” refers to a set of the available characters in a typeface. Each Font Variation includes multiple characters, including many that are not commonly used. To include all of these characters increases the size of the font file, so we offer the ability to choose a subset of characters, per Font Family, in each kit.