From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
When Legendary Super Saiyan Broly uses it, it changes from a small sphere of energy into an enormous energy bomb of devastating power. Not only can he control the size of the attack, but he can also power it up by launching the Ki Blast multiple times into it to push it forward, making it even more powerful and destructive enough to destroy the whole galaxy.
Legendary Super Saiyan Broly used this attack in an attempt to destroy Planet Earth, but Son Gohan, Son Goku, and Son Goten in their Super Saiyan forms counterattacked with the Family Kamehameha in Dragon Ball Z: Broly: Second Coming. As Legendary Super Saiyan Broly kept powering up his attack, Trunks Brief launched his blast at the Omega Blaster to form a barrier. This stopped Legendary Super Saiyan Broly from powering up his attack and caused it to weaken and decrease in size. Super Saiyan Gohan, Super Saiyan Goku, and Super Saiyan Goten then launched all of their power into the Family Kamehameha and broke through the Omega Blaster, blasting Legendary Super Saiyan Broly into the Sun where he was apparently destroyed.
It is named Gigantic Meteor (ギガンティックミーティア, Gigantikku Miitia) in the Budokai video game series and Dragon Ball: Raging Blast. In the latter, it is one of his Super Attacks in his Super Saiyan 3 form. It is a part of the Meteor Attacks.
It is named Gigantikku Miitia (ギガンティック ミーティア, Gigantikku Miitia) in Dragon Ball Heroes.
- Although the Omega Blaster is one of Broly's signature techniques, Goku uses a very similar attack to vaporize the Big Gete Star and Coola at the end of Dragon Ball Z: The Return of Cooler.