Acceleration is a vector quantity. An object undergoes constant , or uniform, acceleration if its velocity changes by equal amounts in equal time intervals.
Average acceleration is the change in an object's velocity during some elapsed time  .
The acceleration of an object at a specific time is called the instantaneous acceleration . A velocity versus time graph can be used to analyze an object's motion. The slope gives the object's acceleration. The area under the curve gives the displacement. The slope of a line segment joining two points on the graph gives the average acceleration during that interval.