What is the service level in Supply Chain?

Service level is the family of metrics that measures how reliably a Supply Chain meets customer demand. The three most common variants are cycle service level (the probability of no stockout during a replenishment cycle), fill rate (the proportion of demand fulfilled directly from stock) and on-time in-full (OTIF, the share of orders delivered complete and on the agreed date). A mature reporting view uses all three at segment level rather than a single headline number, because each one hides a different failure mode when read alone.