In music notation, a sharp is a tic-tac-toe symbol which indicates that a certain note should be raised a half step. If used in the key signature, it means that note should be raised a half-step whenever it is encountered; if used as an accidental, it means that only that note should be changed.

The half-step increment applies whether it changes the note to a "white key" or not. For instance, A-sharp is the same as B-flat, but B-sharp is the same as C.

A sharp looks like this, when used in the key signature and as an accidental with a half note:

----| /----#-----------------------------------------------
    |/             # O                                    
   /|    #          |                                      
 |  |  |            |                                      
  \ |  |