Fire needs three things: oxygen, heat, and fuel. Conventional explosives, like black powder, use a mixture of fuel and oxidizer. On the other hand, a thermobaric bomb uses fuel, a conventional explosive, and picks up an oxidizer as it goes.
Many people have heard of MOAB. Not just the National park in Utah, but the Massive Ordnance Air Blast, better known as the Mother Of All Bombs. MOAB is the most well-known example of a thermobaric bomb.
What Is a Thermobaric Bomb?
A thermobaric bomb uses all the oxygen in an area for its own use. Because the explosion needs oxygen in order to work, a thermobaric reaction actively seeks out oxygen on which to feed. When conventional explosives detonate, a shaped charge acts upon a projectile of some sort. A shotgun shell is an example of this: the primer charge is ignited by the firing pin, which then ignites a contained black powder charge, which ejects pellets from the muzzle.