Definition: Heat Sink

[Lyte]

Heat Sink: A component designed to lower the temperature of an electronic device by dissipating heat into the surrounding air. Some also require a fan which makes them an "active heat sink" while those without a fan are called a "passive heat sink."

I always wondered what these things were... weird name! :p

[Peter]

Very important piece of hardware this is.
Always ensure your heatsink is seated properly on the CPU and that the thermal sticker/paste is in contact with the CPU or it will be fried in no time...