When did the Russian Orthodox Church become autocephalous? What does this mean?

In fact, the beginning of the autocephaly of the ROC can be considered 1448. At that time, when Vasily II the Dark was on the princely throne, Jonah was chosen as the new metropolitan of Kiev at the Moscow local council. This ecclesiastical appointment was remarkable in that it was carried out without the consent of the Patriarch of Constantinople. In general, autocephaly meant gaining independence from the Patriarchate of Constantinople and the possibility of an independent choice of the head of the church through the efforts of the churchmen of their country.