Flat

In music, flat means "lower in pitch." More specifically, in music notation, flat means "lower in pitch by a semitone," and has an associated symbol, which looks like a lowercase "b"; the note A flat is shown in musical notation in Figure 1. Under equal temperament, C flat is the same as, or enharmonically equivalent to, B and F flat is the same as E. There also exist double-flats, which look roughly like "bb" and lower a note by two semitones. Less often one will encounter half, three-quarter, or otherwise altered half.

In musical tuning, flat can also mean "very slightly lower in pitch." If two strings are slightly out of tune, the lower-pitched one is said to be flat with respect to the other.

Figure 1. The note A flat on the treble clef.