Acceleration is the act of increasing speed. When you buy a sports car, you want one that has great acceleration, so it can go from zero to 60 miles an hour in no time.
Acceleration comes from the Latin word accelerationem, which means "a hastening." When you hasten, you hurry, so acceleration is a speeding-up. Maybe you are walking to an appointment and realize you will be late. You pick up your pace — that's acceleration. If the rain on a stormy day begins to come down faster, that too is acceleration. As you can see, acceleration isn't just for cars.