The average velocity is the displacement during a time interval,
divided by that time interval. The direction of the average velocity is
the same as the direction of the displacement vector used to calculate it.The instantaneous velocity is the rate of change of position at a particular instant in time. It can be calculated from the average velocity by making the time interval short. The interval is shortened until we believe that no significant change in calculated average velocity results from further shortening.
We call this the limit of the average velocity, as the time interval approaches zero. The instantaneous velocity is the time derivative of the position.
The direction of the instantaneous velocity is tangent to the trajectory of the object, as it moves through space.