Temperature rise means how much hotter the trace will get with current flowing in it compared to without. You have to decide how much temperature rise your board can handle based on the operating environment and the type of PWB material used. Ten degrees is a very safe number to use for just about any application. If you can live with the trace width required for a ten-degree rise, you are good to go. If you want to try to skinny up the traces, ask for 20 degrees of temperature or more.