Apple ColorLaserWriter 12/600PS - Manual (Page 307)

Suitcases
A font suitcase is a special folder for collections of fonts.
Suitcases provide a convenient way to organize fonts in the same font family.
For example, it’s a good idea to use a single suitcase (called Courier) for all
fonts in the Courier font family—all Courier roman fonts as well as fonts
with names like Courier Bold and Courier Oblique.
Note: PostScript fonts won’t go into suitcases; you can, however, organize
TrueType fonts in suitcases.
285 Using Fonts With the Printer