A collection of submissive's that service one dominant, within a BDSM context.
This can be where a selected group of submissive's will provide their services to one dominant master, though it can include more than one.
Usually the servicing of more than one dominant, is due to the wishes of the primary dominant member.
In a more strict sense, Harem was merely a housing for the woman of the Master, along with the offspring, which included male children.
As well, it wasn't just restricted to the wives, but to the Mistresses as well.