Semitone

In 12-tone equal temperament, a semitone is the interval between any two adjacent pitches.

A semitone is also referred to as a half step or a minor second.

In historical European tunings, a semitone meant "part of a tone (step)," rather than necessarily half, and there were commonly semitones of various sizes.

Context

Introduction to EDO tunings, 12-TET(EDO)