1. A decorative railing together with its supporting balusters, often used at the front of a parapet or gallery.
2. A rail, usually about three feet high, supported by a series of posts (balusters), generally as along the outside edge of a stairway or gallery.

A gallery sometimes refers to a hallway or a covered walkway which has a wall on one side and windows, columns, or a balustrade on the other side.

3. An entire railing system (as along the edge of a balcony) including a top rail and its balusters, and sometimes a bottom rail.
4. A kind of low wall that is placed at the sides of staircases, bridges, etc., and that is made of a row of short posts topped by a long rail along the top.