Thermal Paste/Compound

Thermal Compound (also commonly known as Thermal Grease, Thermal Paste, Thermal Gel, Heat Paste, Heat Sink Paste or Heat Sink Compound) is a thermally conductive adhesive which is applied between your CPU and your cooling heat sink. The grease eliminates the air gap between your CPU and the heat sink allowing for more efficient heat transfer between the two. And the better heat is siphoned away from your CPU, the cooler it can run, extending its life (or the more you can overclock it.)