The United States dropped a MOAB bomb on an ISIS tunnel complex in Afghanistan. So, what exactly does that mean?

Here are a few facts about the weapon:

What does 'MOAB' mean?

Many a headline you’ll see about this story call it the “Mother of All Bombs.” While it fits with the acronym, the military term for the weapon is “Massive Ordnance Air Blast.” The official name for the bomb is a GBU-43B.

How big is it?

The bomb weighs 22,000 pounds, making it the second-largest non-nuclear bomb in the U.S. arsenal. According to How Stuff Works, a GBU-43B is 30 feet long and 40.5 inches in diameter. It was once the largest conventional bomb in the U.S. inventory, but that distinction now belongs to the Massive Ordnance Penetrator (MOP), Air Force officials told ABC News.

ELGIN AIR FORCE BASE, FL - NOVEMBER 21: In this U.S. Air Force handout, a GBU-43/B bomb, or Massive Ordnance Air Blast (MOAB) bomb, is launched November 21, 2003 at Eglin Air Force Base, Florida. (Photo by USAF via Getty Images)

How does it work?

The military said the bomb use in Afghanistan was dropped from a U.S. aircraft. It’s guided by satellite. According to National Review, it can be dropped using a parachute before the satellite system kicks in. How Stuff Works says the bomb explodes about six feet above ground.

Has it ever been used?

No, this is the first combat use of the MOAB since it was developed in the early 2000s. The Associated Press says the Pentagon did a formal review of legal justification for the bomb’s use when it was first developed.

Where did they drop it?

U.S. Press Secretary Sean Spicer said the bomb was used on "a system of tunnels and caves that ISIS fighters used to move around freely." The bomb hit a series of caves in the Achin district of the Nangarhar Province of Afghanistan.

General John Nicholson, commander of U.S. forces in Afghanistan, ordered the bomb’s use.