fonts/knowledge/glossary/terms/variable_fonts/content.md

Variable fonts—or, more specifically, OpenType Font Variations—are a relatively new font format that allow one font file to contain multiple stylistic variations. Weight, width, style, optical size, etc. can then be manipulated by the end user (i.e., designer) and thus avoid the strict delineations of “traditional” fonts.

The first example has a light weight and body-like optical size; the second has a heavy weight and display-like optical size (note the higher contrast); the third also has a similarly heavy weight, but with a body-like optical size.

There are two main benefits offered by variable fonts:

1. The unified delivery of multiple instances—such as different weights, widths, optical sizes—in a single font file that is much smaller than a collection of individual font files.
2. The control given to the user to select values in between the traditional definitions for weight, width, etc.

The variables within variable fonts are controlled by axes or instances. If the type designer, chooses, any variable in the type design can be assigned to a user-controllable axis.