GPU = Graphics Proccessing Unit. Basically just a graphics card for your computer. Can purchase Large like an R9 290X or smaller ones like a 750Ti.

At this point, GPU mining is basically for hobby only.... and for those with cheap electricity. I do have some left over GPU's from my earlier mining days that I would be willing to part with for cheap if you are interested.

Some GPU resources below:

http://www.coindesk.com/information/how-to-set-up-a-miner/
https://www.reddit.com/r/gpumining/
https://litecoin.info/Mining_hardware_comparison#GPU
https://www.cryptocoinsnews.com/guide-setting-gpu-mining-rig/


The current generation of miners run  with ASIC chips which are much more efficient but at the same time much more costly.