The Fifth House of Betazed is a one of the most prominent family organizations on Betazed. One of approximately 20 Houses of Betazed, the Fifth House was one of the most prominent members of that group. (TNG novel Imzadi).
Lwaxana Troi and her surviving daugher Deanna Troi are both members of the Fifth House. Lwaxana would often remind others of her social status as a daughter of the Fifth House, as well as being a holder of the Holy Rings of Betazed and the Sacred Chalice of Rixx. (TNG episodes Haven, Manhunt, Half a Life, and novel Q-in-Law).