What is velocity?

Hint: Speed is defined as how fast an object is moving with respect to time. We use speedometers in our bikes, cars and even bicycles and that speedometer shows us the speed. Instantaneous speed is the speed of a particle or object at that particular instant of time, like whenever you check the speedometer of your vehicle it shows you the Instantaneous speed (speed for that instant of time).

Complete answer:
Velocity is a vector quantity and it is always defined with direction. The magnitude for speed and velocity can be the same but the difference is velocity has a direction coordinate and speed is only defined by magnitude not direction.
In physics we use velocity more than the speed because we always deal with direction along with the magnitude. Velocity is defined as the rate of the change of the position of any object or body with respect to time along with a given direction.
Hence for the answer to our question we can say that the rate of change of the position of any body with respect to time given with a direction coordinate is known as velocity. Whenever there is a motion with a direction, we can always define speed for it.

Note:
Do not get confused between Average and instantaneous speed or velocity, they both are different. Average speed tells you the mean speed for the given interval of time, while instantaneous speed tells you the speed for that particular instant of time. Whenever you see the speed in a speedometer, it is for that particular instant of time hence that is instantaneous speed not average speed.