Where do I get "Gud"?

Where do I get "Gud" ? For years I keep seeing players on forums, videos, Blogs,saying Git "Gud". I searched dozens of hardware sites thinking "gud" was a periphery of some kind but nobody sells "GUD". Then I thought maybe it was software, ya know some kind of gaming app, nope not that either. I then thought it might be some high-power energy drink that makes a players reactions faster but after about 20 hours of searching the 'net I found not a single store that sells "gud"! Please help me! I need to get "gud"! I will by any excess "gud" you may have lying about for a fair price. seems everybody needs to get "gud" and nobody has any, w*f!
Help me get "Gud"!