In this pattern, producers send messages to queues, which hold the messages until subscribers retrieve them. Most message queues follow first-in, first-out (FIFO) ordering and delete every message after it is retrieved. Each subscriber has a unique queue, which requires additional set up steps but makes it possible to guarantee delivery and identify which subscribers received which messages.
This is a Level 3 Documentation and Implementation diagram according to the Salesforce diagram framework.
Learn more by reading the Architect's Guide to Event-Driven Architecture with Salesforce.