SLA based services are services that are based on a service level agreement (SLA). This is a contract between a service provider and the end user that sets out the level of service that the service provider is expected to offer.
They define what the customer is going to receive in exchange for their money, although not how the service will be delivered.An SLA should include a number of different things. It might feature a description of the service, when the service will be available and how quickly it will be delivered when it's needed.
SLA managed services give businesses an agreement for the level of managed IT services that they will receive. Managed IT services are ideal for businesses looking for a reliable service that can be there for them whenever they need it. Maintaining IT systems is essential, and having a clear outline for how the services will be provided is vital.
More info @ What is Service Level Agreement