A shank is an improvised bladed weapon, and can be made from anything. Shanks are mostly made by inmate in prison, whom gather whatever material is available to them and turn them into weapons. Shanks can be made from anything, from a piece of sharp glass wrapped around with fabric, to a razor blade inserted at the end of a toothbrush.
The word shank can be used as a noun, for example "John has a shank ready if anything goes down". Shank can also be used as a verb, as in "Things went down, and John shanked 2 of them."