semitone

A semitone (sometimes called a half tone or a half step) is the distance from a white key to a neighboring black key on the piano keyboard—for example, from G to G-sharp or from E to E-flat. In an octave (from G to the next G above, for instance), there are twelve semitones. Semitones are the smallest intervals that are used intentionally in almost any of the music you'll normally hear. Two semitones equal a whole tone—the distance from G up to A or from E down to D, for example.