A hot shoe is an accessory shoe with added electrical contacts for flash synchronisation. One contact is a round, central dot, surrounded by plastic, the other is the shoe itself. This allows mounting a flashgun without a synchronisation cable.
It is thought that the first hot shoe appeared on the Univex Mercury, in 1938, however hot shoes did not become common until the 1960s. The dimensions of the hot shoe have been standardised, as ISO 518:2006.
Some electronic cameras with dedicated flashguns add extra contacts into the hot shoe to allow the camera and flashgun to communicate, allowing for automatic flash exposure. There is no standardisation between manufacturers for these additional pins or their communication.
Very much later than the introduction of the hot shoe, a plain accessory shoe has become known by the back-formation slang name "cold shoe".