The term "real property" for the purposes of taxation shall be held and construed to mean and include the land itself, whether laid out in town lots or otherwise, and all buildings, structures or improvements or other fixtures of whatsoever kind thereon, except improvements upon lands the fee of which is still vested in the United States, or in the state of Washington, and all rights and privileges thereto belonging or in any wise appertaining, except leases of real property and leasehold interests therein for a term less than the life of the holder; and all substances in and under the same; all standing timber growing thereon, except standing timber owned separately from the ownership of the land upon which the same may stand or be growing; and all property which the law defines or the courts may interpret, declare and hold to be real property under the letter, spirit, intent and meaning of the law for the purposes of taxation. The term real property shall also include a mobile home which has substantially lost its identity as a mobile unit by virtue of its being permanently fixed in location upon land owned or leased by the owner of the mobile home and placed on a permanent foundation (posts or blocks) with fixed pipe connections with sewer, water, or other utilities: PROVIDED, That a mobile home located on land leased by the owner of the mobile home shall be subject to the personal property provisions of chapter
84.56 RCW and RCW
84.60.040.