These terms appear in every reliability discussion:
SLI (Service Level Indicator): A metric. " latency" or "error rate" or "availability percentage."
SLO (Service Level Objective): A target for an SLI. " latency < ms" or "% availability."
SLA (Service Level Agreement): A contract with consequences. "If availability drops below %, customer gets credits."
Relationship: SLI measures reality. SLO is your internal goal. SLA is your external commitment (usually less aggressive than SLO).
Example: Your SLO might be % availability, but your SLA promises % to give you buffer.