Service Level Agreement (SLA)
Represents a commitment between a service provider and one or more customers and addresses specific aspects of the service, such as responsibilities, details on the type of service, expected performance level (e.g., reliability, acceptable quality, and response times), and requirements for reporting, resolution, and termination.
Source: NIST NIST SP 800-47 Rev. 1 under service-level agreement
A formal agreement between a service provider (whether internal or external) and their client (whether internal or external), which covers the nature, quality, availability, scope and response of the service provider. The SLA should cover day- to-day situations and disaster situations, as the need for the service may vary in a disaster.