From Quake Wiki
In Quake, gibs are utilized for an overkill event, also known as gibbing, bringing an entity's health below a certain threshold, for example -40 for a player, or -60 for a Shambler. To gib is a verb to describe such an overkill.
The gib death manifests itself in the entity's body reduced to a severed head and some assorted chunks of flesh, which are flung in random directions with considerable force, spewing blood and bouncing around. Upon coming to a rest, gibs disappear after some time, except for heads.
There is also the sister function of ThrowHead which throws a head gib model unique to the entity that was gibbed. Head gibs are considered on par with a normal monster corpse, and thus take longer to be removed.
Apart from the gib model string, these functions may also take the entity's health at the moment of death, which is used in some simple velocity calculation (via VelocityForDamage) to change the gibs' initial speed, thus representing the severity of the gibbing. Note that this health is normalized to -99 by Killed in combat.qc), though VelocityForDamage is able to take lower values.
Another form of gib occurrences in Quake is the use of SpawnMeatSpray which specifically calls the zombie projectile gib model zom_gib.mdl. These small gibs are the chosen projectile of zombies. SpawnMeatSpray is also called during a melee attack by Ogres, Fiends and Shamblers.
- Rotfish in stock Quake cannot be gibbed.
- MultiDamage handling functions (which collect and apply shotgun damage as a single take) employ some imperfect code that is unable to reliably gib several targets at once.
- gib2.mdl represents a dismembered human torso. Oddly enough, gibbing a scrag yields as much as three of these. In addition, gibbable rotfishes in the Scourge of Armagon spawn one too.