Service Level Indicator - specific metric that measures an aspect of service performance. Like using a speedometer to measure how fast your service responds to users.
Common SLIs include response time (how quickly API calls return), error rate (percentage of failed requests), and availability (percentage of time the service is working).
SLI (Service Level Indicator) is a reliability concept, not a single cloud service. All major clouds provide monitoring/observability tools (metrics, logs, traces) that you use to define and measure SLIs such as availability, latency, and error rate.