A Service Level Agreement (SLA) is a formal document that outlines the expected level of service between a service provider and a client. It specifies the quality, availability, and responsibilities of the service, ensuring both parties have clear expectations. SLAs are commonly used in various industries, including IT, telecommunications, and customer support. SLAs often include metrics for measuring performance, such as response times and resolution times for issues. They also detail the consequences if the agreed-upon service levels are not met, which helps maintain accountability and fosters trust between the service provider and the client.