The Albin House at night.
In the context of Ghost House's story, a capital-H House is a supernatural entity that functions as its own personal pocket universe, operating on its own scale of time and space separate from its original universe.
A House typically spawns in response to strong emotions tied to a location, or (in some cases) when a dramatic event involving many lives happens in a space. Despite the name, a House's form is not limited to specifically a house, like the building - as long as its 'anchor', or its original location, exists in a physical space, the House is free to take whatever shape it needs to exist. These Houses commonly belong to the ghost from whom the feelings come from, though many ghosts are contained in these places. The older the House's age, the more ghosts from lost explorers wind up ballooning it, causing it to both obtain and use a lot of energy to exist.
The only House seen in the BCU is specifically the Albin house, the setting for both Ghost House games. However, it is confirmed there are other Houses that exist out in the Garden.
Houses can spawn in any universe, and functionally act as a small pocket universe, appearing to operate beyond logical concepts of time and space in their home universes. Hence, they typically get the designation PV-XXXXX. One way a House can be destroyed is by encouraging the spirits tying the House to existence to move on to the "afterlife". By doing so, the House no longer has a ghost to shape itself around, disassembling the PV. This also happens to segments of the House that are tied to ghosts with stronger abilities in these sections, though these sections will reappear in the House over time. EX: Klair Marsh encouraging Lydia Roe to move on disassembled the library in the Albin House, but that library gets rebuilt not long after the ghost leaves.
Additionally, Houses employ many forms of defense mechanisms - the first is utilizing ghosts of living beings that died in these spaces, whether in the initial incident that spawned a House or later on as the location baits victims in and harnesses energy from them. The more ghosts a House has, the more difficult for it to continue existing. A secondary way - though considered somewhat unethical - of dispelling a House is to starve it out. The less power a House has, the less it can do. When it drops to low enough levels of energy, a House can even be restrained to its original location only, unable to suspend itself externally.