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, decoupled communication. On AWS, similar patterns are commonly built with SNS (pub/sub fanout) 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 Kafka-like pub/sub streams; OCI also offers Notifications for simpler pub/sub alerts.