In music, flat, or bemolle (Italian: "soft B") means "lower in pitch". In music notation, the flat symbol, ?, derived from a stylised lowercase "b", lowers a note by a half step (semitone).Intonation or tuning is said to be flat when it is below the intended pitch.
The order of flats in the key signatures of music notation, following the circle of fifths, is B?, E?, A?, D?, G?, C? and F? (mnemonics for which include Battle Ends And Down Goes Charles' Father and Before Eating A Doughnut Get Coffee First).
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Under twelve-tone equal temperament, C? for instance is the same as (or enharmonically equivalent to) B? (B-natural), and G? is the same as F? (F-sharp). In any other tuning system, such enharmonic equivalences in general do not exist. To allow extended just intonation, composer Ben Johnston uses a sharp as an accidental to indicate a note is raised 70.6 cents (ratio 25:24), and a flat to indicate a note is lowered 70.6 cents.
Double flats also exist, which look like (similar to two flats, ??) and lower a note by two semitones, or a whole step. The Unicode character ? (U+1D12B) in the Musical Symbols block represents the double-flat sign.
A quarter-tone flat or half flat, indicating the use of quarter tones, may be marked with various symbols including a flat with a slash () or a reversed flat sign ().