mudflap

/ˈmʌdˌflæp/
noun
  1. A piece of rubber or plastic hanging behind a vehicle's wheel to stop mud, water, or stones from being thrown up.
    • He replaced the old mudflap with a new one that had a logo on it.
    • Mudflaps are required on large trucks to protect other cars from debris.
    • The truck's mudflap was torn off after hitting a pothole.