California Code, Revenue and Taxation Code - RTC § 20508

“Residential dwelling” means a dwelling occupied by the claimant as the principal place of residence, and so much of the land surrounding it as is reasonably necessary for use of the dwelling as a home, owned by the claimant, the claimant and his spouse, or by the claimant and some other individual, and located in this state. It shall also include a residential unit in a cooperative housing corporation (as defined in Section 216(b) of the Internal Revenue Code 1) occupied by the owner of shares or a membership interest in such corporation as his or her principal residence, mobilehomes which are assessed as realty for local property tax purposes and the land on which situated, houseboats, and other similar living accommodations, as well as a part of a multidwelling or multipurpose building and a part of the land upon which it is built. It shall also include premises occupied by reason of the claimant's ownership of a dwelling located on land owned by a nonprofit incorporated association, of which the claimant is a member, when such association requires the claimant to pay a pro rata share of the property taxes levied against the association's land. It shall also include premises occupied by a claimant wherein he is required by law to pay a property tax by reason of his ownership (including a possessory interest) in the dwelling, the land, or both. It shall also include a dwelling unit which is a mobilehome owned by a claimant, subject to property taxation pursuant to Part 13 (commencing with Section 5800), and located on land which is owned or rented by such claimant. (Owned includes the interest of a vendee in possession under a land sale contract but not the interest of the vendor, the interest of the holder of a life estate interest, but not the interest of a remainderman, and of one or more joint tenants or tenants in common. Except in the case of an unrecorded land sale contract, ownership must be evidenced by a duly recorded document.)