Speed is a scalar quantity that refers to "how fast an object is moving." Speed can be thought of as the rate at which an object covers distance.

Velocity is a vector quantity that refers to "the rate at which an object changes its position." Velocity can be thought of as the rate at which an object covers displacement. Imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. While this might result in a frenzy of activity, it would result in a zero velocity because this person has had 0 displacement.