It is a covered walk in a religious institution having an open arcade opening onto a courtyard. There will be a wall around the outside of the cloister
Cloisters were for monks to walk during bad weather. If a church or cathedral doesn't have cloisters it means that it never had monks attached to it - or perhaps the cloisters were destroyed during...
No, Orthodox churches are where persons of Greek or Russian Orthodox faith worship. Like the Church of England, the Orthodox also separated from the Roman Catholic Church on matters of doctrine.