A Ka-bar is the 7" fighting / utility knife used by the US Marines in World War II. The name came from the manufacturers of the knife, the Union Cutlery Company, who stamped their trademark into the mark side tang. More than 1 million of these knives were manufactured during the WWII. The Ka-bar remains a favorite, virtually obligatory piece of equipment with US Marine infantry at present, although the US Marine Reconnaissance units generally prefer the Gerber Mark II.

The KA-BAR company was founded in 1898 as Tidioute Cutlery Company; following its financial collapse and take-over it was renamed the Union Cutlery Company. KA-BAR was initially a trademark but in 1952 the company renamed itself KA-BAR Cutlery Inc.

The origin of the word KA-BAR is uncertain. The company claims it is a corruption of "Kill a Bear", an ability ascribed to the knife by a customer. A competing etymology, displayed in a museum at the Marine Corps Officer Candidates School (OCS) in Quantico, VA, is that it originally stood for "Knife Attached - Browning Automatic Rifle."