The Canon EF 100-400 mm f/4.5-5.6L IS USM lens, a high-performance L-series telephoto zoom lens known for its versatility in sports and wildlife photography, featuring a 4-stop Image Stabilizer (IS), Ultrasonic Motor (USM) for fast autofocus, fluorite/UD elements for sharp images, and compatibility with Canon EF-mount DSLRs. It's a compact, powerful option with advanced coatings (ASC, Fluorine) to reduce flare and smudges, offering superb image quality and handling for demanding situations.