in the context of
photography: that interesting metal slide-like thing you can find on the top of nearly all
SLR. It works as a
hardpoint for mounting a
flash, and at the same time provides the flash with the
synch signal that it needs to fire when the shutter opens.
A basic hotshoe simply short-circuits the outer metal brackets with the central post. Some hotshoes have additional contacts, meant for interfacing with
dedicated flashes.
All hotshoes have the same measures, which means that (at least for basic functionality) you can mount almost any flash on any camera - with the exception (thank SharQ) of the evil Minolta brand, that uses a nonstandard hotshoe.