This is a replacement Nissan Inner Fender Shield Retainer Clip which fits Nissan models such as the 300ZX (Z31) and Pathfinder (WD21).

This black, plastic two piece push-in clip hold the front inner fender liners to the body. Due to age, heat and normal wear and tear, these clips often break when released. These Push-Type Clips also offer a variety of other applications when you're looking to discretely hold trim or wires in place throughout your vehicle.