Angel

In the context of the Angel state, the term refers to deceased characters who have been allowed to retain their physical bodies in Other World, identified by the signature golden halo floating above their head. Goku, Vegeta, Pikkon, and the Ginyu Force have all appeared in this state at various points. This Angel designation is distinct from the angel attendants like Whis and Vados, who are a separate celestial race.

No, the Angel state is not a race. It is a designation given to a deceased individual who is permitted by King Yemma to retain their physical body in Other World rather than being sent on to Heaven or Hell. The signature golden halo above the head is the visual indicator of this status.

Goku has already entered the Angel state multiple times in the series whenever he has died. After sacrificing himself during the Cell Games he spent seven years in Other World as an Angel, training under Grand Kai and alongside Pikkon, which is where he developed Super Saiyan 3. The state preserved his physical body so he could continue training in the afterlife.

No, the Angel state itself does not multiply combat strength. The user's power level remains exactly what it was at the moment of death. Any subsequent power increase comes from training in Other World, not from the state itself.

Returning to the living world is restricted and requires special permission. Under normal circumstances an Angel is confined to Other World. Techniques like Instant Transmission combined with King Yemma's approval can allow temporary returns, as Goku demonstrated when he visited Earth during the Buu Saga.