The sharp of any note increases its pitch by a semitone. It is the opposite of a flat, which reduces pitch by a semitone. Sharps are indicated in standard music notation by the symbol #.
On a piano keyboard, each black key is a sharp of the white key on its left, and, likewise, is a flat of each white key to its right. Thus, for example, the black key to the immediate right of C is C sharp and the black key to the immediate right of D is D sharp. However, the white notes C and F can also be considered as sharps of the respective white keys to their immediate left.
All scales have at least one sharp except for C major, which has no sharps or flats. The largest number of sharps a scale can have is seven, which is for the C sharp major scale.