A Meteor Smash is a move in any characters arsenal that sends an opponent straight down or at a diagonal angle in the least. Mostly these types of maneuvers are Down Aerials if not some being Forward Aerials. Not all characters have a intentional meteor, so there are Unconventional Meteors.
Unconventional Meteors only happens on grounded opponents. Great for limiting your opponents mobility or when your opponents waiting on a ledge.