A motu proprio (Latin "on his own impulse") is a document issued by the Pope (or by a monarch) on his own initiative and personally signed by him.
When issued by the Pope, a motu proprio may be addressed to the whole Church, to part of it, or to some individuals.
The first motu proprio was issued by Pope Innocent VIII in 1484. It continues to be a common form of Papal rescripts, especially when establishing institutions, making minor changes to law or procedure, and when granting favours to persons or institutions.
Read more about Motu Proprio: Effect, Form, Notable Examples, Other Uses of The Phrase "motu Proprio"