Vasectomy is a surgical procedure in which the vasa deferentia of a man are cut for the purpose of sterilization.

There are some variations on the procedure such as no-scalpel (keyhole) vasectomies, in which a sharp hemostat, rather than a scalpel, is used to puncture the scrotum. Another type of vasectomy which may reduce the risk of chronic pain is called an "open ended" vasectomy. A "normal" vasectomy typically seals both ends of the vas deferens with stitches, heat, metal clamps or a combination, after cutting. The open-ended vasectomy obstructs only the top end of the vas deferens. With this method sperm leaks out from the lower severed end of the vas deferens and into the scrotum, thus hopefully avoiding a build-up of pressure in the epididymis. The likelihood of long-term testicular pain from "backup pressure" seems to be reduced using this method.

From http://en.wikipedia.org/wiki/Vasectomy