1. not closed or barred at the time, as a doorway by a door, a window by a sash, or a gateway by a gate: to leave the windows open at night.
2. (of a door, gate, window sash, or the like) set so as to permit passage through the opening it can be used to close.
3. having no means of closing or barring: an open portico.
4. having the interior immediately accessible, as a box with the lid raised or a drawer that is pulled out.
5. relatively free of obstructions to sight, movement, or internal arrangement: an open floor plan.