When a Cocker Spaniel is mated to a poodle to produce a cockapoo this is known as a first generation cross and is referred to as an F1.Sometimes a cockapoo is mated back to one of the parent breeds either the spaniel or poodle and this produces an F1b.
F1 Cockapoo + F1 Cockapoo = F2.
F1 Cockapoo + Poodle = F1b.