My understanding it's the other end of a one way USB cable. Normally the cable is attached like your mouse or keyboard, or commonly these days USB C, but if you are plugging in USB and it's not USB C but the cable unplugs at either end, one will be USB A and the other USB B so you can't put it in backwards like you could if they both has USB A.

Early android smart phones used USB B micro or mini, but printers have no need to keep the plug small.