Service Level Objective - specific measurable target for service performance. Like setting a goal to answer customer calls within 30 seconds, 95% of the time.
A web service sets an SLO of responding to API requests within 200 milliseconds for 99% of requests.
An SLO (Service Level Objective) is a reliability target you define for a service (for example, latency or availability). It is not a single cloud product; all major clouds support measuring and alerting on SLOs via their monitoring/observability services, but the SLO itself is a practice/contract within SRE and service management.