Shortened form of Channel Lock Plier, more correctly called Tongue and Groove Plier. A pliers design that facilitates a tongue and groove system where the upper jaw is fixed and the lower jaw adjusts to close on the object without requiring the handles to be opened along an axis to be placed on the object. These pliers generally have serrated jaws and high leverage which makes them a powerful tool for securing piping, conduit, nuts, bolts, as well as anything where you need a very strong grip, but the ability to quickly release and reset. Also commonly refered to as pump pliers due to their ability to be "pumped" closed with one hand. Commonly used for plumbing and electrical work.
480 - 20.25 inch BigAZZ® Tongue and Groove Plier @ Channellock
The term comes from one manufacturer, Channellock Tools : Pliers, Wrenches and Screwdrivers, but is usually applied generically. One can even have a Channellock Crescent wrench, and Crescent Channel Lock pliers.