A fender liner is a protective panel that lines the inside of a car's wheel wells. It's also known as an inner fender liner or splash guard.
Purpose
Protects from debris: Prevents mud, rocks, and other debris from damaging the car's body and internal components
Protects from water: Prevents water from seeping into the engine bay or suspension components
Protects from corrosion: Prevents rust and corrosion build up