Normally in Physics we use metres per second (m/s) for speeds and velocities, and this gives us a very odd looking unit for acceleration.
e.g. A Tour de France cyclist accelerates from 10 to 15 m/s in 10 s.
Yes, that's right! Acceleration is normally measures in metres-per-second-per-second! All this means is a change in velocity per second. Sometimes you may see accelerations written as m/s² rather than m/s/s. They are the same thing.
Notice that the change in velocity is given by final velocity - initial velocity.