0 "Open floor plan" means that instead of each room being a separate room with four walls and a door or two, several of the rooms (perhaps the kitchen, dining room and living room) are really just different areas within one big room. It is "open" because ther are no walls or doors dividing the different areas. I think a vaulted ceiling is arched or curved; that is, the ceiling is higher in the center than at the edges.
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