thermal design 
Thermal design specifications are guidelines that Intel and PC makers use to handle heat removal from notebooks. In general, the more powerful a microprocessor is, the more power it consumes and the more heat it gives off. Thermal design guidelines are aimed at designing low-power-use chips. If a chip uses low-power design, then the speed of the chip can increase without giving off more heat than the system can tolerate, in other words, without breaking the permissible thermal "envelope."