In most cases, the term refers to the rear bumper assembly — the large, prominent plastic panel at the back of a vehicle, extending from the left taillight to the right taillight.

Specifically, it covers the following:

What you see (the outer cover): The painted plastic shell, usually made of PP (polypropylene) or ABS plastic. In everyday language, when people say "replace the rear bumper," they typically mean this outer plastic cover.

The structural part behind it (the reinforcement): Hidden inside the plastic cover is a rear bumper reinforcement beam (usually made of metal). If that beam is bent, it's specifically referred to as the "rear crash bar" or "rear impact beam."

Its official name: On vehicle registration certificates and insurance policies, it's officially called the "rear bumper assembly."

Its main functions are not to withstand heavy impacts, but rather:

Low-speed cushioning: Absorbs energy during low-speed collisions (e.g., backing into a wall or a minor rear-end bump), protecting the trunk and chassis from damage.

Pedestrian protection: The plastic material causes less leg injury to pedestrians than metal would.

Aesthetics and aerodynamics: Hides wiring and components while helping to manage airflow under the vehicle.