The Combat Knife is a fighting knife designed solely for military use and primarily intended for hand-to-hand or close combat fighting.
Since the end of trench warfare, most military combat knives have been secondarily designed for utility use (clearing foliage, chopping branches for cover, opening ammunition crates, etc.) in addition to their original role as close-quarter combat weapons, and may be referred to as "fighting-utility knives". On the other hand, military knives that are intended primarily for use in a role other than combat are typically referred to by their primary role, such as "utility knife" or "survival knife".
In Mortal Kombat
Combat Knives are a signature weapon of the Black Dragon Leader, Kano. Almost all kinds of knives and sharp weaponry has been a part of Kano's arsenal. (Such as Butterfly knives, Bowie knives, Throwing Knives, Elbow Blades and Boot Blades.) In most games his knives have been holstered in sheathes on his boots.
By Mortal Kombat 11, his knives named in-game as Shanks are Gear Items that he can customize. With a wide variety of knife variants and designs to choose from. He also shows off his shanks in some of his intros and victory cinematics.
The knife is also used by some Special Forces soldiers as a backup weapon in Mortal Kombat X. It is best seen in Chapter 1 during the Story Mode. Guest character Jason Voorhees, in one of his intros also has him pulling out a knife from his neck, showing off his inability to feel pain and his status as an immortal revenant.
In MK11's Story Mode, a combat knife is used a few times in cutscenes. In Cassie's Chapter, she makes use of it to battle some of the Netherrealm Armies' Demons. While in Past Sonya's Chapter, one of the Special Forces Soldiers tries to futilely fend off Geras with a combat knife, getting in a few swipes and stabs before ultimately being killed rather gruesomely off-screen.
In his return as a guest character in Mortal Kombat 11, The Joker also makes use of a knives alongside his rather vast arsenal. Notably he uses it in one of his intros, where he runs his thumb across the edge till it bleeds and uses his blood to paint his face with his signature "smile". He also makes usage of knives in his Fatal Blow.