wall. An erection of stone, brick, or other material raised to varying heights, esp. inside or surrounding a building, for privacy, security, or enclosure.

ancient wall.A party wall that has stood for at least 20 years, thus giving each party an easement right to refuse to allow the other party to remove or substantially change the wall.

party wall.A wall that divides two adjoining, separately owned properties and that is shared by the two property owners as tenants in common. — Also termed common wall. [Cases: Party Walls  1–10. C.J.S. Party Walls §§ 1–59.]

“There appears to be no precise legal definition of the term ‘party wall.’ Four possible meanings are as follows: (a) Tenancy in common: the two adjoining owners are tenants in common of the wall. (b) Divided: the wall is divided longitudinally into two strips, one belonging to each of the neighbouring owners. (c) Divided with easements: the wall is divided as in (b), but each half is subject to an easement of support in favour of the owner of the other half. (d) Ownership subject to easement: the wall belongs entirely to one of the adjoining owners, but is subject to an easement or right in the other to have it maintained as a dividing wall.” Robert E. Megarry & M.P. Thompson, A Manual of the Law of Real Property 303–04 (6th ed. 1993).
[Blacks Law 8th]