From IT Nation Wiki
SLA Service Level Agreement An SLA is a formally negotiated agreement between two parties. It is a contract that exists between customers and their service provider, client or between service providers. It records the common understanding about services, priorities, responsibilities, guarantee, and such — collectively, the level of service. For example, it may specify the levels of availability, serviceability, performance, operation, or other attributes of the service like billing and even penalties in the case of violation of the SLA. Historically, SLAs have been used since late 1980s by fixed line telecom operators as part of their contracts with their corporate customers. More recently, Information Technology departments in larger enterprises have adopted the idea of using service level agreements with their customers — users in other departments within the same enterprise — to allow for comparing the delivered quality of service with the one promised and potentially consider the alternative of outsourcing IT services to an external company. The technical specifications of an SLA are commonly described through either a Service Level Specification (SLS) or a Service Level Objective (SLO). An SLS is intended as an operational guideline for the implementation of the service, and an SLO is a subset of an SLS containing some service parameters and goals to be achieved by the SLS.