Coolers (Heatsink + Fan)
The fan in the middle of the graphics card is referred to as active cooling, as it involves moving parts.
In most cases a cooler is simply a heatsink with a fan attached to blow air across the surface of a heat sink, increasing the ability to dissipate heat. Graphics card coolers are typically applied to the graphics processor, because the graphics processor is the hottest component on the video card. There are many aftermarket models available today, which can be used to exchange/upgrade factory-installed coolers. These are also known as VGA coolers.
However, VGA coolers do not always apply only to the graphics processor. In many cases, a single, large heat sink/cooler will apply to both the graphics processor and the graphics memory at the same time, cooling everything.
This is a comprehensive single-slot graphics cooling solution. It covers both the graphics processor and the graphics memory, but does not occupy more space than what a single expansion slot offers.
If a VGA cooler is small enough that it doesn't encroach on the adjacent slot - and another card could be put in that slot without physically interfering with it - it is called a single-slot cooler.
If a VGA cooling device is too large to allow another card to be put into the adjacent slot, it is referred to as a dual-slot cooler. Typically, dual-slot coolers are designed to exhaust hot air out of the back of the case through the second slot, which is a good way to prevent the heated air from increasing the temperature inside of your computer case. In such a case, a radial fan is used, which uses its blades to push air away sideways rather than blowing air downwards.