Latency

Uptime

The percentage of time a service is reachable and responding correctly over a given window.

Downtime

Any period during which a service fails to respond, returns errors, or is so degraded it is unusable.

SLA (Service Level Agreement)

A formal contract between a service provider and a customer that defines minimum service levels and the con…

SLO (Service Level Objective)

An internal reliability target — for example, "99.9% of API requests succeed within 500 ms over a rolling 3…

SLI (Service Level Indicator)

The raw measurement that an SLO is calculated from — request success ratio, latency percentile, or freshnes…

MTTR (Mean Time To Resolve / Recover)

Average time between an incident being detected and the service being fully restored.