Observability is the practice of instrumenting systems to measure their internal state through external outputs, enabling teams to understand and debug complex distributed systems. Unlike traditional monitoring which tracks predefined metrics, observability provides the ability to ask arbitrary questions about system behavior using logs, metrics, and traces as core telemetry signals. The key difference lies in unknown-unknowns: monitoring answers questions you already know to ask, while observability helps you explore questions you didn't anticipate, particularly critical in microservices architectures where emergent behaviors and cascading failures are common.