SLA stands for Service Level Agreement. SLA is agreement between a hosting user and its hosting provider. SLA defines the level of service that has to be provided by the hosting provider. For example hosting SLA may guarantee that the hosting customer will have 99.9% Server Uptime or that in event of server hardware failure the faulty hardware will be replaced within 2 hours. SLA may also define penalty clause in case the SLA guarantees are not met.