Non-quitter, but covered is a slang term used to describe an individual that performs oral sex to completion but uses a condom or other protective device.
Non-quitter, but Covered (NQBC)
More About Non-quitter, but Covered (NQBC)
Non-quitter, but covered is one of the various ways that oral sex can be described. This variety implies that it is not a bareback blow job because there is a protective device used. This also means that there is no spitting or swallowing of ejaculate.