Seisin
Seisin (or seizin) is a legal concept that denotes the right to legal possession of a thing, usually a fiefdom, fee, or an estate in land. It is similar, but legally separate from the idea of ownership.
The term is traditionally used in the context of inheritance law in the form of "the son and heir of X has obtained seisin of his inheritance", and thus is a term primarily concerned with conveyancing. The person holding such estate is said to be "seized of it", a phrase which commonly appears in inquisitions post mortem. It has varying relevance in modern legal systems, with distinctions between Common law and Civil law jurisdictions.