A "5.1 system" refers to a type of surround sound audio setup commonly used in home theaters and audio systems. It consists of six channels: one subwoofer and five main speakers. The five speakers are typically arranged to create a surround sound experience, with three in the front (left, center, right) and two in the rear (left and right). The subwoofer is responsible for low-frequency sounds, enhancing the overall audio experience by providing deep bass. This configuration allows for a more immersive listening experience, making it popular for watching movies and playing video games, where sound directionality adds to the realism.