Answers:
Shank means 2 things
1. A "homemade" or more likely "cellmade" weapon used to stab, like a knife. Can be anything.... a filed toothbrush, a piece of the bedposts, piece of plastic.... whatever you could fashion into a knife-like shape and keep hidden.... When you stab someone they say ""you shanked him." I believe this term derives from the handle, as anything you can grab something by is a shank in old European English. Like a knife handle or a trunk of a bush or plant.
2. A bad kick.... if a football or soccer player kicks the ball and it goes sideways instead of straight, the term is "he shanked it".... a British slang term used often in the USA. Also used in Golf, for the same thing, a drive that goes sideways or not where it was intended to.
An undie grundie or de-panting is called a shanking too, I believe, but I am not 100% sure on that. If its not shank its something close. I'm sure I'm missing some here but I am also sure some dope will go to wikipedia then copy paste it and look like a genius when we all know hes a mental midget.