In architecture and construction, that wall is most commonly called a parapet.
However, the specific name can change depending on where the wall is located and its primary purpose. Here are the most common terms:
1. Parapet
This is the standard term for a low wall built along the edge of a roof, bridge, or balcony. Its main job is to prevent people from falling off the edge and to provide a protective barrier.
2. Guardrail (or Handrail)
While often made of metal or wood, a solid wall serving this purpose is frequently referred to as a guard. In building codes, “guards” are required whenever there is a significant drop (usually 30 inches or more) to protect occupants.
3. Balustrade
If the “wall” is decorative and made up of individual pillars (balusters) topped by a rail, it is called a balustrade. You see these often on grand staircases or classical balconies.
4. Knee Wall / Pony Wall
In interior design, a short wall that only goes up to about waist height (and doesn’t reach the ceiling) is often called a knee wall or a pony wall. These are common in lofts or along staircases to create a partition without blocking the view.
5. Retaining Wall
If the wall is holding back soil or earth on a slope to prevent a drop-off in the landscape, it is a retaining wall.
(Courtesy: OpenAI)