H is for Hot Shoe
Frequently on top of cameras is a clip of sorts. Most frequently, there is a flash unit pressed into the clip for taking photos under low-light conditions.
This clip is called a shoe. I have no idea why.
When hand-held cameras became popular, manufacturers provided additional equipment (typically flashes, but also rangefinders and light meters) that could be bought to go with that camera. Each add-on was specific to that camera, and most times could not be used with any other camera.
The standardized shoe on top of the camera made it possible for the extras to be moved between different cameras of different makes and models. It became possible for companies to specialize in devices that would work with any camera (provided it had a shoe) and not have to also make a camera as well.
The “Hot” shoe took the concept one step further. It has an electrical contact that is triggered when the shutter is activated, making it possible for a flash placed into the shoe to strobe simultaneously with the shutter.
Suddenly, manufacturers could make elaborate flashes that would also work with any camera and always be synchronized with the shutter for the optimal photograph.
Modern camera shoes are far more complicated and have gotten back to being more specific to the camera. Today’s cameras are computerized with sensitive electronics. Extra contacts allow the camera’s computer to communicate with and control the attached flash as needed.
Because of the new complexity, one has to exercise caution when switching flashes between cameras. The wrong flash can destroy the sensitive electronics of a camera. So be careful.