More completely, Commodore 1520
A small, really small, printer which you could connect to the C64 and VIC 20 computer, and probably to many other Commodore machines.
It was like a miniature version of those giant roll plotters where you have a meter-wide roll of paper being driven in and out of the plotter, and a penhead that moves trasversally (this design is inevitably less precise than a flatbed plotter).
Commodore brilliantly took this concept and hit it with the bonsai stick: the 1520 prints on a roll of paper about 5 inches wide, using 4 tiny ballpoint pens.
The many applications of such a device do not exist at all: too small for technical drawings, too small for writing reports, too expensive for everyday printing (and slow, BTW).
It was essentially a toy, and I greatly desired it. It was probably good I never bought one.