The First House of Betazed was apparently one of the most important families in Betazoid culture. "By the First House" was a type of expletive among Betazoids. (TNG novel: The Battle of Betazed) The First House is of course implied by the existence of the Fifth House of Betazed, established in the TNG episode "Haven". The full significance of these houses in Betazoid history or culture has never been explicitly explained in canon.