only meet 900 units of that order, your fill rate is 90%. In statistics, notably in queuing theory, service rate denotes the rate at which customers are being served in a system. It is the reciprocal of the service time. For example, a supermarket cash desk with an average service time of 30 seconds per customer would have an average service rate of 2 per minute. In statistics the Greek letter is used for the service rate. Terminology The term "Service Level Agreement" (SLA) is frequently used for all aspects of a service level, but in more precise use one may distinguish: Service Level Indicator (SLI): measures of service level, like availability (uptime); Service Level Objective (SLO): objectives based on these indicators, like 99.95% availability; Service Level Agreement (SLA): contract based on these objectives; a sample clause may be "if availability is 99% to 99.95% in a given month, the customer gets 10% off their monthly bill". SLIs form the basis of SLOs, which in turn form the basis of SLAs. If an SLO is missed, customers will typically receive a credit or rebate, as stipulated by the SLA. A missed SLO is sometimes casually referred to as an SLA violation, but this is actually within the scope of the SLA; if an SLA itself is violated (e.g., by not giving a rebate for a missed SLO), it is instead likely to result in a court case for breach of contract. See also Inventory Service level agreement (SLA) Service level indicator (SLI) Service level objective (SLO) Service level requirement (SLR) Stockout References Further reading Tempelmeier, Horst, Inventory Management in Supply Networks, Norderstedt (Books on Demand) 2006, Inventory Customer service