An upper receiver is a key component of a firearm, specifically in AR-15 style rifles. It houses the bolt carrier group and the charging handle, playing a crucial role in the cycling of the action. The upper receiver is typically made from aluminum for durability and lightweight performance. Upper receivers can be customized with various accessories, such as sights, rails, and handguards. They come in different configurations, including flat-top and A2 styles, allowing users to tailor their rifles to specific needs or preferences. This versatility makes the upper receiver an essential part of modern sporting rifles.