A more thorough explanation:

Legal seisin is the possession of a freehold estate in land, which means ownership. It can also refer to the completion of the ceremony of feudal investiture, which admitted the tenant into freehold. In Louisiana law, it refers to the right of universal successors to own and possess a person's estate directly and immediately upon that person's death.

For example, if John inherits a piece of land from his father, he has legal seisin of the land, which means he has the right to possess and own it. However, if John has not yet entered the land, he only has seisin in law, which means he has the right to immediate possession of the land but has not yet exercised that right.

Legal seisin is different from actual seisin, which is the physical possession of the land, and equitable seisin, which is the possession or enjoyment of a property interest or right enforceable in equity.