Publisher-Subscriber (Pub/Sub) vs Observer Pattern?

Observer is synchronous and tightly coupled. Pub/Sub is asynchronous and decoupled via an event broker.

In Observer, the subject holds direct references to observers and calls their methods. In Pub/Sub, publishers and subscribers don't know about each other. They communicate through a message broker or event bus (e.g., RabbitMQ, Kafka), allowing distributed, asynchronous communication.