I believe, not sure though, that mosque is just the English way of saying Masjid, which means, where you do sajda(prostration)... Mosque is not the original word... The original is Masjid.
They are the churchs of the Muslims. Mosque is not even the right word, the real word for the Place of Worship of Muslims is MASJID. The mosque/masjid is sacred because it the house of worship and...
When intending to remain in a mosque for certaing period for worship. This is called "Al-E3tekaf" or "الاعتكاف" and those wroshipers are called عاكفون "akefoun" In Quran: وَلَا...