From TF2 Wiki
Gibs or "giblets" are the bits and pieces of a players' body that are left after the player has been blown up by an explosive, such as rockets (from a Soldiers Rocket launcher or an Engineers Level 3 Sentry gun) or a Demomans' Grenades or Sticky bombs. A player will only gib on a direct hit from one of these weapons. To lighten the mood after you are gibbed, the game will point out any body parts that appear on the Deathcam.
Giblets include the torso, hands, heads, feet, arms, legs, liver, appendix, pancreas and other assorted organs, as well as various accessories such as eyeglasses, helmets, gas tanks and bullet shells (see below for list by class). In Party Mode, gibs are replaced by humorous, censor-appropriate objects such as balloons and unicycles.
The term gibs also encapsulates debris left by destroyed buildings, broken sappers, broken razorbacks and the fallout from the explosion upon the attacking teams' victory on the final stage of a payload map.
The term 'gib' can also be used as a verb, e.g. 'gibbing' someone, meaning reducing an enemy to gibs by blowing them up with a rocket or grenade.
Players can gib themselves on command by entering explode into the console (similar to suiciding by entering kill).
It should be noted that the in-game gibs, with the exception of the Soldier, do not show the player models' final designs. For example, a gibbed Scout has a different shoe design, and his socks have stripes. Also, if a player wearing an unlocked hat is gibbed, their hat will either disappear, or appear alongside the default hat in the player's gibs.
A Comprehensive List of Gibs
|Spy||Torso, Head, Arm, Two hands, Leg, Thigh|
|Engineer||Shoulder, Head, Helmet, Hand, Arm, Knee, Leg|
|Demoman||Torso, Head, Arm, Hand, Leg, Thigh|
|Pyro||Torso (two parts), Head, Gas tank, Two hands, Leg|
|Soldier||Shoulder, Head, Arm, Two feet, Helmet, Two pouches|
|Sniper||Torso, Head, Hand, Hat, Leg, Foot, Glasses|
|Medic||Torso, Head, Two hands, Two legs, Glasses, Bottom|
|Scout||Torso, Head, Arm, Hand, Leg, Cap, Foot, Headset, Bottom||As well as after the release of the Uber update, when Scout is gibbed in-game, there is a chance of Archimedes the Dove flying out of him. Seen here.|
|Heavy||Torso, Head (Upper Jaw), Foot, Hand, Leg, Bullet, Bottom|
Party Mode Gibs
Party Mode servers and censored versions of Team Fortress 2 have completely different types of gibs.
(The Sapper also has 2 suction-cup like parts which is uses to drain energy. These also appear as gibs.)