How Do You Define Acceleration?

Acceleration means rate of change of velocity.

As a word "acceleration" refers to the act of accelerating or the process by which one accelerates. In Physics however, acceleration refers to the rate of change in velocity of an object in relation to time. As a simple way to understand acceleration consider the formula of acceleration, where it is nothing but the final speed less the original speed divided by time. Speed is different from acceleration and is calculated based on what distance has been covered divided by the time taken.  

The simple formulae of acceleration given above can be applied to most situations. Say a car moves from a signal to the other side of the junction. All the variables of speed, time taken, initial speed, are all available and all that is needed is an application of the formulae.

Other useful equation of motion are

v=u+at
s=1/2(u+v)t
s=ut+1/2a(t squared)
(v squared)=(u squared) + 2as

Where v is final velocity, u is initial velocity, s is displacement, t is time.