Seisin (or seizin) is the legal possession of a feudal fiefdom (i.e., an estate in land). It was used in the form of "the son and heir of X has obtained seisin of his inheritance", and thus is effectively a term concerned with conveyancing in the feudal era. In the feudal age, the king alone "owned" all the land of England by his allodial right; all his subjects merely held tenures in fiefs, that is to say estates-in-land.