A wall, rampart, or elevation of earth or stone to protect soldiers. (Merriam -Webster)
A low wall or railing to protect the edge of a platform, roof, or bridge. (Merriam – Webster)
A parapet is a low wall along the edge of something high such as a bridge or roof. (Collins Dictionary)
A low wall along the edge of a roof, bridge, etc. (Cambridge Dictionary)
A low protective wall along the edge of a roof, bridge, or balcony. (Oxford Dictionaries)
A protective wall or earth defence along the top of a trench or other place of concealment for troops. (Oxford Dictionaries)
Parapet Collapse: An Old Danger for Today’s Firefighters.