Umm al-Mu'mineen means 'Mother of the Believers' . This was the title of the Prophet's wives; ( sura 33 ayah 6 stipulated that they could not marry after the Prophet's death because all of the believers were their spiritual children.
MOTHER OF THE BELIEVERS
Meaning of MOTHER OF THE BELIEVERS in English
Advanced Islamic English dictionary. Расширенный исламский словарь английского языка. 2012