Definitions for "Semitone"
Half a tone; -- the name commonly applied to the smaller intervals of the diatonic scale.
The smallest interval on the piano, a semitone is the distance between any two consecutive keys. Semitones can be found from a white key to a black key, from a black key to a white key, and in the few cases where there is no black key in between two white keys, from a white key to another white key.
Distance between two adjacent notes on a keyboard, same as half-step.