FlatIn music, 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 B and F flat is the same as E. There also exist double-flats, which look roughly like "bb".
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.
See also sharp
The word flat also has other, unrelated uses: