^ I'll probably suck at explaining this, and will leave it for Vivaglam or CC or Sam12 or Littleathquakes or Gabriel29 to explain better lol.
Main Victoria Secret Angels are: Adriana, Alessandra, Doutzen, Miranda, Rosie, and Candice, and Behati.
Victoria Secret Bombshells: Erin, Lindsey, Lily A, maybe Chanel?
Victoria Secret Angels are the main contract girls. The money makers. They promote and are the faces of the brand. They attend majority of the launch events together or separately and are in the annual fashion show. They are the veterans.
The Bombshells: I don't know if there is a standard definition for them but from what I see, I think they are like the VS Angels Jr. They aren't the main contract girls, but they attend events, and launches for the brand. I would believe that they don't get paid as much, and they also attend castings for the annual show.