CPU fan
Read the Safety Procedures. Very Important!!!
There is numerous types of Processor CPU fans. There is too many to show or explain here. Here is a picture of one fan (but there are others)
They are used to keep the processor/cpu cool. If the processor/cpu overheats, it will cause the processor/cpu to malfunction. They are either mounted on top of the processor/cpu or mounted to the side of it. The power connector is connected to the motherboard.