Acceleration

Acceleration is the speed gained over time; for example, a sports car is significantly faster than a normal car due to its enhanced acceleration.

The calculation is the change in Velocity divided by Time. The standard way of writing it is m/s, or meters per second.
If we simplify it, is it m/s^2 or meters per second squared, something to keep in mind is that both velocity and acceleration are different, as if we take a car and drive it on a road, and take photos every second and overlay them together, it looks like the car is getting further and further away each photo. 

This is an accurate depiction of what acceleration looks like. This style of diagram is named 'the oil-drop diagram' because it looks like an oil drop.

Another thing to keep in mind is that velocity is a vector, meaning it has a direction associated with it, indicating the direction in which the object is moving.
But if the object is slowing down instead of speeding up, then it is decelerating.