Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-46.170.65.33-20130801062633/@comment-13899768-20130802001208

I think it's a two part definition.

A) We learned in season 2 that an omega is the lone wolf, one without a pack.

But what we learned in the most recent episode is from Ethan, and I think he was actually comparing it to an actual wolf pack:

B) Omegas are the bottom of the totem pole. Usually the weakest, which means last to eat etc.

By that definition, and Ethan's story, we can conclude that they were the weakest in a pack of killers (Therefore Omegas) because they had not yet mastered the merge.