Google Cloud's messaging service that allows applications to communicate asynchronously. Like a mail system where applications can send messages without waiting for replies.
An e-commerce site uses Pub/Sub to notify inventory systems when orders are placed, without making customers wait.
Google Cloud Pub/Sub is a managed publish/subscribe messaging service for asynchronous communication. On AWS, similar patterns are commonly built with SNS (pub/sub fan-out) and SQS (durable queues). On Azure, Service Bus topics/subscriptions provide durable pub/sub, while Event Grid is optimized for event routing. On OCI, Streaming provides durable event streams (Kafka-like), while Notifications provides pub/sub-style push notifications; the closest match depends on whether you need durable messaging, event routing, or streaming.