Board Thread:General Discussion/@comment-31283382-20131101162239/@comment-5553481-20140719223724

The only CONFIRMED Vasto Lorde is Tier Harribel, I'd assume that the 4 top Espada are Vasto Lorde, rest Adjuchas with Aaroniero Arruruerie being the only Gillian.

Now, onto the question from OP - "what is the difference between Arrancar and Vasto Lorde???"

1. Arrancar is a "transformation" that apparently any hollow can achieve through tearing off their masks, which would bring out a question - why don't all of them do?

2. Vasto Lorde is a final step of hollow "evolution" (not counting arrancar), which basically goes something like this: hollow eats hollows, becomes Gillian who eats Gillians, becomes Adjuchas who eats Adjuchas (if he stops eating he will go back to being Gillian forever), he then becomes Vasto Lorde, who AFAIK doesn't need to eat anymore.