The black keys on the keyboard are named after the white keys and because of this there are always two possible way to name a black key as there is a white key to the left or the right of the black key. In spite of the two different names the black keys note remains the same.
If you name the black key after the white key to its left it is written with a sharp (#) or after the white key to its right is is written with a flat (b).
So for example the black key between C and D is called either C sharp or D flat.
