SLA (Service Level Agreement) is a contract between a service provider and customer that defines expected service standards. It specifies measurable metrics like uptime percentage, response times, resolution times, and availability hours. Common SLA metrics include 99.9% uptime (allows 8.76 hours downtime yearly), ticket response within 24 hours, or issue resolution in 48 hours. SLAs protect both parties by setting clear expectations and penalties for non compliance. Essential for cloud services, IT support, and B2B relationships.