Design pattern that prevents cascading failures by stopping calls to failing services. Like having electrical breakers that shut off power to prevent house fires.
Microservices implement circuit breakers to avoid overwhelming failing payment services during high-traffic events.
Circuit Breaker is an application design pattern (not a single cloud service). You typically implement it in code (e.g., Resilience4j, Polly) or via service-mesh/API gateway features that can detect failures and stop or shed traffic to unhealthy upstreams.