♭

Glyph origin
Originally a lowercase b written with a round loop (the so called "round B" or "B rotundum") to distinguish from a lowercase b written with a square loop ("square B" or "B quadratum"), when the only notes used in (Western) music were what are now considered C, D, E, F, G, A, B-flat and B. The round B was used for the former and the square B for the latter. The round B was then later generalized as the symbol for flat notes.

Symbol

 * 1)  A flat; a bemol (a note one semitone lower).

Usage notes
In general typography, the symbol is usually written as lowercase b.

Related terms

 * (double flat)