A more thorough explanation:

Definition: Seisin is a legal concept that refers to the possession of land. It originated from early English property law and still influences certain concepts in the modern law of real property. In the past, a landholder was considered "seised of" his estate, which is similar to ownership but has some differences. Seisin was passed through a ceremony called "livery of seisin".

For example, if John owns a piece of land, he has seisin of that land. This means he has the right to possess and use the land, and to exclude others from it. However, if John leases the land to Mary, she has seisin of the land during the term of the lease. This means she has the right to possess and use the land, but John still owns it and can take it back after the lease ends.

Another example is if a person inherits a piece of land from their parents. They have seisin of the land because they have the right to possess and use it. However, if there are any legal disputes over the land, they may need to prove their seisin through the proper legal channels.

These examples illustrate how seisin relates to the possession of land and the rights that come with it. It is an important concept in real property law and can affect how ownership and possession are determined.