lordship itself: the rightful authority of the Lord to be obeyed
This is the abstract sense of the word: not a person and not a being, but the quality of being lord, the authority that belongs to a master and is owed obedience. It is the noun form of the title Lord (κύριος), the way holiness is the noun form of holy.
In both places it appears this way it is something people refuse to honor. Jude and 2 Peter describe teachers who throw off all restraint and treat the Lord's authority with contempt. The word names exactly what they are rejecting: the right of the Lord to command them. Most scholars read this as the authority of Christ himself, the very lordship the false teachers deny by living as a law to themselves.
It is no accident that the same writers pair this rejection of lordship with insults flung at angelic beings. The picture is of people so sure of their own freedom that they will not bow to the Master above them or show respect to the powers around them.