A railing or barrier installed along the edge of roads, bridges, stairs, or platforms to prevent people from falling.
From guard (to protect) plus rail (a bar or barrier), a compound noun meaning a protective railing. Common in transportation and safety contexts since the 19th century.
Guardrails are one of engineering's quiet heroes—they prevent thousands of deaths yearly, yet we barely notice them until someone crashes into one, showing how good design becomes invisible.
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