Kafka Messages

Im a bit confused on the concept of a "message" in Kafka. How does this differ, if at all, from a message in RabbitMQ? It seems to me that Kafka is better suited for very write intensive "messages" like log data but RabbitMQ may be a better fit for traditional "messages"… i.e. "Product Purchased" or "User Registered" message. Can someone please clarify on this?

Also can anyone provide some concrete use cases?

Thanks for the help