Font cartridge
A ROM module that slotted into the front of a printer and gave it letterforms it did not carry on board.
The first HP LaserJet (1984) shipped with exactly one typeface: Courier, 12 point, portrait. Anyone who wanted Times or Helvetica — in one specific size and one specific orientation — bought a cartridge and pushed it into a bay on the front panel. HP named them after letters: cartridge B, F, Z. Each held finished bitmaps in ROM, one image per point size, because the printer had neither the processor nor the memory to scale anything itself.
The alternative was soft fonts, downloaded over the cable into printer RAM and gone at the next power cut, plus third-party modules like Pacific Data Products' "25 in One!" that crammed dozens of faces into a single cartridge. Dot matrix printers had the same idea on a smaller scale. PCL 5 and the LaserJet III (1990) made fonts scalable inside the printer, and once TrueType and PostScript moved typography back onto the computer the cartridge had nothing left to do.