GPU--graphics processing unit...aka, the graphics chip/card that is the counterpart of the CPU or Central Processing Unit.
https://en.wikipedia.org/wiki/Graphics_processing_unit
As far as fixing it, depends on your hardware and what you mean by fixing it and what is wrong with it. If you mean replacing it, then if you have a desktop it is a matter of buying a new card and installing it, along with drivers and such(if your hardware has the space and slots...). If you are talking about a laptop, then likely you are talking about replacing the entire machine. If you are talking about updating drivers, then checking with your manufacturers website or the website of Nvidia or AMD for latest ones....
So depends....