It could refer to various clips or magazines
Clip - A simple, disposable narrow spring-lined channel-rail in which cartridges are supplied for military weapons. The shooter positions the clip vertically above the firearm's magazine, then pressing down with the thumb, slides the cartridges from the clip and down into the magazine. Also: Stripper Clip or Charger.
Magazine - A spring-operated reservoir compartment for holding cartridges waiting to be fed into the chamber of a repeating firearm. May be built in or removable.
http://www.hallowellco.com/abbrevia.htm
