The actual name of this bomb is Massive Ordnance Air Blast (MOAB) but it has long since been known as the Mother of All Bombs because it is the largest non-nuclear weapon the U.S. has produced. Today it was dropped in Afghanistan, the first time the bomb has ever been used in combat. From CNN:

The bomb was dropped by an MC-130 aircraft, operated by Air Force Special Operations Command, according to the military sources.

They said the target was an ISIS tunnel and cave complex as well as personnel in the Achin district of the Nangarhar province.

CBS News reports the plan to drop the bomb has been in the works for months:

“The strike was designed to minimize the risk to Afghan and U.S. Forces conducting clearing operations in the area while maximizing the destruction of ISIS-K fighters and facilities,” the Pentagon said in a statement, using the term for the Islamic State’s Afghanistan branch…

The Afghanistan strike had been in the works for a number of months, [CBS News’ David] Martin reports. The weapon was brought into Afghanistan specifically for this mission.

This map shows the location where the bomb was dropped:

This History channel clip gives some detail on the development of the MOAB and includes video of a test: