What is the name given to running fingers length of piano keys?

The term you are referring to is called "glissando". It is a musical technique where a performer rapidly slides their finger(s) across the keys of a piano, producing a smooth, continuous change in pitch. Glissandos can be performed in either direction, upwards or downwards, and can cover a wide range of notes. They are often used to create a sense of movement or transition in a piece of music.