It is a Latin phrase that means freely and voluntarily. It means by my decision, my will, my judgment, on my initiative (without anyone asking me, demanding it or asking me). By choice, of your own free will.
It is a Latin formula for "voluntarily, on his own initiative." Motu is by "inclination to, movement towards" and proprio by "particular, distinctive".
Motu proprio : Bula pontificia or royal card thus issued.
MOTU PROPRIO-Is a Latinism which means of its own free will, i.e., without that medium coercion, even without request. It is very common to hear people and even great communicators say erronéamente: " of mutual itself. " The mutual is indeed a contract.