A more thorough explanation:

Definition: Post disseisina is a legal term that refers to a writ used to recover land by a person who had previously recovered the land from a disseisor by a praecipe quod reddat or on a default or reddition, but who was again disseised by the same disseisor.

Example: John sued Tom for the recovery of his land, which Tom had taken from him by force. John won the case and got his land back. However, Tom again took the land from John by force. In this case, John can use the post disseisina writ to recover his land again.

The example illustrates how post disseisina is used to recover land that has been taken by force by the same person who had previously taken it and was sued for it.