A protective barrier, usually made of metal or wood, placed along the edge of a road or highway to prevent vehicles from veering off. The car skidded on the icy road but was stopped by the guardrail, preventing it from going over the cliff.
A safety barrier installed on the edge of a platform, walkway, or other elevated area to prevent people from falling. The construction site was equipped with guardrails to ensure the workers' safety while working at heights.
A rule, guideline, or limit that prevents undesirable actions or decisions. Clear financial guardrails were set to keep the project on budget.