Sharp

In music, sharp, dièse (from French), or diesis (from Greek) means higher in pitch and the sharp symbol raises a note by a half tone. Intonation may be flat, sharp, or both, successively or simultaneously. More specifically, in musical notation, sharp means “higher in pitch by a semitone (half step),” and has an associated symbol (♯), which may be found in key signatures or as an accidental, as may flats.
Under twelve-tone equal temperament, B sharp, for instance, sounds the same as, or is enharmonically equivalent to, C natural, and E sharp is enharmonically equivalent to F natural. In other tuning systems, such enharmonic equivalences in general do not exist. To allow extended just intonation, composer Ben Johnston uses a sharp to indicate a note is raised 70.6 cents (ratio 25:24), or a flat to indicate a note is lowered 70.6 cents.
In tuning, sharp can also mean “slightly higher in pitch” (by some unspecified amount). If two simultaneous notes are slightly out of tune, the higher…