1a key on a typewriter or computer keyboard used to cause the carriage or cursor to move backwards.
2a device on a video recorder or camcorder which produces a slight backward run between shots to eliminate disturbance caused by the interruption of the scanning process: [as modifier]:begin with a few seconds of static shot, remembering to allow for backspace time
move a typewriter carriage or computer cursor backwards.
backspace in other Oxford dictionaries
Definition of backspace in the US English dictionary