In the old days you’d have called this the ‘hotshoe’, since it’s traditionally been provided to offer a connection for external flashguns, but although it’s still used for that it has other uses today. It can also used to attach accessories like Nikon’s ME-1 external microphone, remote control units and even Nikon’s GP1A GPS receiver. It’s also a handy attachment for small LED panels for video work – these are self-powered and don’t connect electrically to the camera, and simply use the accessory shoe as a convenient mounting point.