The term "backline" refers to the equipment and instruments used by musicians in a band, particularly those that are not part of the front-line performance. This includes items like amplifiers, drums, and keyboards, which are essential for producing sound but are typically positioned behind the performers on stage. In the context of live music, the backline is crucial for ensuring that the sound quality is optimal. It can also refer to the team responsible for setting up and maintaining this equipment during concerts and events, allowing the front-line musicians to focus on their performance.