Meteor Smash, called Graviton Hammer (グラビトンハンマー Gurabiton Hammā) in Japan, is an unblockable move introduced in Tekken 3 for Bryan Fury's moveset. There is a weaker but faster version of this move called Gravity Blow. Meteor Smash, like other unblockable moves, is not for high level play. A simple side step, jab, or even a backdash (because the move has short range) is all that is needed to avoid it.
Meteor Smash is known as "Graviton Hammer" in Japanese; it is unknown why Meteor Smash's name was differentiated from that of Gravity Blow.