BLU-118/B Thermobaric Weapon (Source globalsecurity.org)
Abstract: The BLU-118/B nomenclature was first reported on 21 December 2001, and this weapon is clearly unrelated to the BLU-118 500 lb. napalm canister used during the Vietnam war.
The BLU-118/B is a penetrating warhead filled with an advanced thermobaric explosive that, when detonated, generates higher sustained blast pressures in confined spaces such as tunnels and underground facilities. The BLU-118/B uses the same penetrator body as the standard BLU-109 weapon. The significant difference is the replacement of the high explosive fill with a new thermobaric explosive that provides increased lethality in confined spaces.
Read the full text: http://www.globalsecurity.org/military/systems/munitions/blu-118.htm