The white keys are named A, B, C, D, E, F, and G. The notes between—the black keys—are the ones with compound names. The note between A and B is called either A-sharp or B-flat, and in all but formal music theoretic discussions, the two terms are interchangeable. (In fact, this note could also be referred to as C double-flat, and similarly, A could be called G double-sharp, but this is an even more theoretical usage.) Sharp means high, and flat means low. B-flat is the note one semitone lower than B; A-sharp is the note one semitone higher than A.
