A more thorough explanation:

Assisa de morte antecessoris is a legal term that refers to an action for the recovery of land belonging to the claimant's ancestor. It was a procedure introduced in Henry II's reign for the trial of questions as to the ownership or possession of lands held by free tenure.

For example, if a person's ancestor owned a piece of land, but it was taken away from them, the person could use the assisa de morte antecessoris to try and recover the land. The court would determine who had the rightful claim to the land based on evidence presented.

This procedure was abolished in the early 19th century, but it was an important part of English legal history and helped establish the rights of landowners.