That is how fast the pixels change. The slower the response time the more motion blur theres going to be. For gaming the lower the response time the better but anything under 8 should be fine. GTG is how they measure it. theres also black white black but the one you should pay attention to is GTG. Oh yeah, and different panels have different response times. TN panels have the lowest (some are 1ms GTG) but also the colors on those panels aren't as good. I like IPS panels the best because they have around 6-7 ms GTG usually and have nice colors/viewing angles.