The selected region highlights a smoke-style translucent matte back cover designed for modern smartphones. These types of cases are popular for their slim profile and the "smoke" finish that provides a sleek look while offering protection against drops and scratches.
Based on the distinct camera module cutout, this specific case appears to be for a Samsung Galaxy S21 Ultra. Similar styles are also available for a variety of other phone models.
Product Features
Material: Typically a combination of a hard polycarbonate (PC) backplate and flexible TPU (thermoplastic polyurethane) edges for shock absorption.
Design: Features a matte translucent finish and often includes a raised bumper around the camera lenses for added protection.