What is "cook off"

vb. 1 (context transitive US military English) To pull the pin from a grenade and wait two or three seconds before throwing. 2 (context transitive US military English) As with above, except to unintentionally wait so long that the grenade detonates. 3 (context transitive chemistry military English) To cause an accidental detonation of explosives, especially due to excess heat. 4 (context intransitive chemistry military English) To accidentally detonate, especially as the result of excess heat.