Subsetting is the practice of creating a “subset” of a font—a file that contains a custom (and usually limited) collection of glyphs.

There are numerous scenarios where subsetting may be desirable:

1. When a font delivery service wishes to optimize the file size of a web font.
2. When a foundry wishes to offer a limited character set as a trial font.
3. When a developer wishes to strip unrequired languages from a web font.
4. When a foundry (or designer) wishes to distribute a collection of glyphs for a specifics use, as was the way with small caps or stylistic sets prior to the arrival of OpenType.
5. When a foundry wishes to create a customized collection of glyphs (perhaps with modifications) for a client.

There are many online services that can generate subsets for the user on-the-fly, but it’s important to consider whether a particular font license allows for subsetting or not.