A fender liner is a protective cover that sits inside the wheel well of a car to shield the inner parts from dirt, water, and other debris that might kick up from the road. Full definition
In some vehicles, the front inner fender liner may inadvertently rub against the brake lines, resulting in the risk of a brake line leak, break failure and a crash. (indianainjuryandfamilylawyerblog.com)
Its tires are coated in several inches of thick mud, which caused the rear fender liners to pop out. (automobilemag.com)