Velocity is the rate of change of the position of an object. velocity is a vector quantity, specifying velocity is equivalent to a specification of object's speed and direction of motion. Speed describes only how fast an object is moving, whereas velocity gives both how fast and in what direction the object is moving.
For example, if a car is said to travel at 80 km/h, its speed has been specified. However, if the car is said to move at 80 km/h to the south, its velocity has now been specified because we know both speed and direction of motion.