Gib

A Gib is piece of a soldier, usually after blown off with an explosive weapon or a powerful weapon. Killing someone in this manner is know as "gibbing." The only games in which the player can gib enemies at any given time is Call of Duty: World at War and possibly Call of Duty: Black Ops, but gibs can be seen in Call of Duty 4: Modern Warfare, Call of Duty: World at War, and Call of Duty: Black Ops.

Call of Duty 4: Modern Warfare
The only instance in Call of Duty 4: Modern Warfare where gibbing is seen is when the player snipes off Imran Zakhaev's arm in the level One Shot, One Kill.

Call of Duty: World at War
In Call of Duty: World at War the player can gib throughout the entire game, decapitating and blowing off limbs, or even blowing people in half. Gibbing is also required to complete the multiplayer challenge Gib Factory on Call of Duty: World at War. Weapons that can gib are as follows: all explosives, MG42, FG42 (single player only), M1919, Type 99 (single player only), PTRS-41, M1897 Trenchgun, Double-Barreled Shotgun and by running over someone with a Tank.

Call of Duty: Black Ops
Gibbing can be seen in the reveal trailer for Call of Duty: Black Op. It is unkown at the moment if you can gib throughout the entire game.

Trivia

 * On occasion, when enemy's head is blown off in Call of Duty: World at War, the enemy will shriek in agony for a few seconds after, even without a mouth/head to scream with. This is most likely a simple designer error.
 * It is incredibly easy to gib on Nazi Zombies, as gibbing can be done with a mere Kar98k. Only the .357 Magnum, the Colt M1911, and the M2 Flamethrower cannot gib without Insta-Kill.
 * On the iPod Touch And iPhone Game COD: Nazi Zombies, gibbing is required for the Grinder Achievements.
 * On the Nazi Zombies map Der Riese, the Bowie Knife is able to gib zombies.
 * Gibbing cannot be done on the Wii version of Call of Duty: World at War.
 * In World at War, if a dead body is shot in the face, it will be blown apart. Although after awhile, the face will return to normal.
 * Sniper rifles can completely blow off an enemies jaw.
 * Players cannot blow off an enemies head in multiplayer, but it can be done in Nazi Zombies and the singleplayer campaign.

Video
http://www.youtube.com/watch?v=7WIteICViiE