ELI5: What Is the Publish-Subscribe Messaging Pattern?

Introduction

Used in microservices architecture (a method of designing software applications that is rapidly growing in popularity), the publish-subscribe messaging pattern is a form of asynchronous communication where messages are published to a topic and received – in real-time – by consumers who subscribe to the topic.

Now, what does that really mean? What are the advantages of publish-subscribe? How can you explain it to someone non-technical?