SLI (Service Level Indicator): metrics to quantify the performance of a service, e.g. availability, latency, data quality, data freshness, etc.
SLO (Service Level Objective): desired target for a single SLI; mostly for internal use, no financial commitments. E.g. service availability 99.95% over a year, 100ms for p99 latency.
SLA (Service Level Agreement): externally visible contract about the SLO. If violated, there are consequences, like refunding or paying a penalty. E.g. if service availability is lower than 99.95%, service provider will pay a penalty of $X Million.
