A more thorough explanation:

eadem persona cum defuncto

In the past, when someone died, their property would be passed down to their heir. The law considered the heir to be the same person as the person who died. This means that the heir had full ownership of the property, just like the person who died did.

For example, if John died and left his house to his son, the law would consider John's son to be the same person as John. This means that John's son would have full ownership of the house, just like John did when he was alive.