The black keys on a piano are called the sharps and flats. They are also known as the enharmonics.
There are 88 keys on the piano. Of these, 52 are white and 36 are black. The white keys are called naturals. The black keys received their name because each is either a sharp note or a flat note depending on in which key the piece is written. An A sharp, for example, is also a B flat. The composer can use either designation. This also explains the origin of the black key's second name, enharmonics. An enharmonic is a note of a given pitch that goes by two different names.