To the Dead, a Domain is an area that's "owned" - or at least claimed - by certain Concord. In this case, "ownership" implies that the Concord has either gained a monopoly on the Haunts within their Domain, or has earned proper Tribute {or at least an understanding} from Wraiths of other Concords whose Haunts fall within that area.

The word Domain is also used to describe the area - most often a Haunt - that a Wraith, or Circle of Wraiths, have claimed as their own. Their claim usually comes from the area being their Haunt, which may be an Anchor Haunt or Ghost Haunt, but the Domain may also be an area that they've taken control of through other means.

In either case, their Concord lays claim to this Domain through the presence of its Wraiths, but may or may not consider that land theirs to do with as they please. Some Concords are very liberal with the notion of "owner's rights," while others - most notably The Order - insist that it all belongs to them.

As Haunts form the building blocks of Domains, gathering and holding Haunts is the primary goal of many Concords within a Necropolis. This activity has become known as The Game of Houses, though no Wraith is absolutely certain why this name was put upon it, or when. It's just another one of those things which make enough sense for Wraiths to take it for granted, and cause enough headaches to leave well enough alone.