Question

what is acceleration?​

Answer 1

Acceleration is the rate of change of velocity. Usually, acceleration means the speed is changing, but not always. When an object moves in a circular path at a constant speed, it is still accelerating, because the direction of its velocity is changing.

Answer 2

The rate of change in velocity in unit time of called Acceleration. Acceleration is a vector quantity.

$acceleration = \frac{change \:in \: velocity}{time \: taken \: for \: change}$