What is "khurramites"

The Khurramites ( Khorrām-Dīnān, meaning "those of the Joyful Religion"; Khurramiyya) were an Iranian religious and political movement with its roots in the movement founded by Mazdak. An alternative name for the movement is the Muḥammira (, "Red-Wearing Ones"; in Surkh-Jāmagān), a reference to their symbolic red dress.