distinguish themselves from conventional explosive weapons by using atmospheric oxygen, instead of carrying an oxidizer in their explosives. They are also called high-impulse thermobaric weapons (HITs), fuel-air explosives (FAE or FAX) or sometimes fuel-air munitions, heat and pressure weapons, or vacuum bombs. They produce more explosive energy for a given size than do other conventional explosives, but have the downside of being less predictable in their effect.

Source of Definiton