A type of camera flash. Speedlite is the trade name for Canon's line of external flashes for use with their EOS line of cameras. Nikon Corporation's uses "Speedlight" (note spelling) brand for their flashes.
Note that while "Speedlite" is most commonly associated with Canon's flash series, it is not a registered trademark, and was also used by Ricoh.
The spelling "speedlight", while currently primarily used by Nikon, is also a generic term.