Sharp
In music, sharp means "higher in pitch by a semitone." The note C sharp is shown in musical notation in Figure 1. Under equal temperament, B sharp is the same as C, and E sharp the same as F.
In musical tuning, sharp can also mean "very slightly higher in pitch." If two strings are slightly out of tune, the higher-pitched one is said to be sharp with respect to the other.
Figure 1. The note C sharp on the treble clef.
See also: flat.
The word sharp has other, unrelated uses: