The Mercies of a Masjid

What exactly is a masjid? Is there a difference between a masjid, musallā, and jamāt khāna, etc? These are questions which need detailed discussion. Nowadays, in the west, many Islamic Centers being managed include, among other things, a prayer hall, musallā, or jamāt khāna. Some communities rent an industrial unit, a store front, a house, or an apartment in which members of the Muslim community gather to perform congregational prayer (and in many cases social activities). Many communities actually have purchased property which they consider their masjid. Which of the above can technically be considered a masjid, and what are the related rulings?