Velocity is defined as a measure of the distance an object travels in a stated direction in a given length of time.
Thus velocity is speed in a stated direction. Velocity is referred to as a vector quantity because it possesses both size and direction, the size being speed. Where speed only tells us how fast or slow an object is moving it gives no reference of direction velocity is used as a more complete measure as it not only gives speed but also the direction.
Two cars could be travelling with the same speed of 100 km/h on a motorway. However, by stating one car is travelling 100 km/h north and the other 100 km/h south do we realise they are travelling in opposite directions, thus the velocity gives a better indication of the motion.
The average velocity of an object can be determined from the equation below: