TDP stands for thermal design power or, depending who you ask, thermal design profile. The TDP number tells you the maximum heat a computer chip, such as a CPU or GPU, can use in watts. It also is often used as a basic indicator of power consumption.
More watts equals better performance, but also higher temperatures and more power consumption. PC OEMs can sometimes lower the TDP on a chip to increase battery life on a laptop or raise it up to boost speed.
When it comes to CPU shopping, check out your CPU’s TDP to determine what kind of CPU cooler you need and to make sure you have a PSU (power supply unit) that provides enough juice.
This article is part of the Tom's Hardware Glossary.