Software Engineering · Architecture
Services communicate by publishing and subscribing to events rather than calling each other directly — a producer emits 'something happened' and consumers react without the producer knowing who they are.
Example: An order service publishes an `OrderPlaced` event; separate inventory and billing services consume it independently.
In practice: The decoupling is real and valuable, but it makes tracing a request through the system significantly harder — you trade temporal coupling for debugging difficulty.