Ok as far as I know, UMA stands for Unified Memory Architecture... This is when the Graphics Card is built into the Motherboard, and isn't separate, like it normally is. This is never normally a good option to take, because it can cause a lot of problems in terms of memory usage, and if you play a lot, the motherboard WILL get fried pretty quickly. Anyway, the k55 is a very basic laptop and isn't really for gaming. You won't be satisfied with the AMD A8-Series processor and the 1366 x 768 resolution. If you want to play games, don't settle for a K series, look into their G series.
Also, Brett is right, you won't really get anything for the price you want to pay. You're going to have to up your budget if you want decent laptop performance.