Meaning
Service Level Indicator; a carefully measured metric that tracks real-world service behavior, such as latency or error rate.
Three examples from work
Metric definition
SREWhat is our SLI for checkout reliability?
LeadThe percentage of HTTP 200 responses versus total requests over a rolling 30-day window.
Review sync
DevOpsOur latency SLI dropped slightly during peak evening hours.
DevLet's check if the database query cache hit ratio degraded.
Hierarchy explanation
Junior DevHow do SLI, SLO, and SLA relate to each other?
MentorSLI is what you measure; SLO is the target you set; SLA is what you promise in legal contracts.
Pronounce each letter: 'S-L-I'. The simple rule of thumb: SLI is the measurement, SLO is the goal, SLA is the legal agreement.