Both are fine. "Award" is usually for recognising achiement. It could be a certificate, or something like a box of chocolates A "prize" is something you might get for an acheivement, winning a contest, or for being lucky. It is usually something physical like a box of chocolates. A certificate isn't a very good prize. So, a prize is often an award and an award often comes with a prize. What you call it is usually up to the person giving it out!