A variant on the Type 1 font format, Multiple Master fonts allow the user greater control over a font's appearance. For example, rather than having fixed steps between weights bold, ultrabold and black, users can adjust the weight themselves to any point on the scale between regular and black.
Created by Adobe, Multiple Master fonts are made up of three files (a .pfb, a .pfm and a .mmm) and require Adobe Type Manager to be installed.