Accidentals are symbols that indicate the alteration of the pitch of a tone.
A sharp raises the pitch of a tone by a half step.
A flat lowers the pitch of a tone by a half step.
A natural is used to cancel a sharp or flat.
A double flat lowers the pitch of a tone by two half steps.
A double sharp raises the pitch of a tone by two half steps.
A natural is sometimes used in conjunction with a sharp or flat in order to cancel one of the flats/sharps of a double sharp or double flat.
Notice in the musical examples above, the accidentals are always placed in front (to the left) of the notes they affect. On the other hand, when writing about music, the word or symbol representing the accidental follows the letter name (e.g., “A flat” or “G#”).
The black keys of the keyboard can be labeled with either flats or sharps.
