Rates are a way of referring to a players upload/download rates set between their computer and the server. With relevance to First Person Shooter games such as counterstrike this is set within the games console/settings/config so as to allow a degree of control depending on the speed/quality of your internet connection (originally designed to help 56k gaming be a reality.)

Can be used in negative such as “Rates Mate RATES!!!” to imply that you have deliberately misconfigured your settings to allow you some advantage in the game.

There are several scripts including some built into mani admin mod that allow control of rates, automatic setting when a player joins and monitoring.