A more thorough explanation:

dum non fuit compos mentis

dum non fuit compos mentis is a legal term that means "while he was of unsound mind." It refers to a writ that allows heirs to recover an estate that was transferred by someone who was not mentally capable of making such a decision.

For example, if a person with a mental illness or dementia transferred their property to someone else, the heirs could use dum non fuit compos mentis to recover the property. This writ is used to protect people who are not capable of making sound decisions due to their mental state.