Microsoft Azure Service Bus is a cloud-based messaging service that enables applications to communicate with each other reliably and securely. It allows different software components, whether they are on-premises or in the cloud, to send and receive messages, ensuring that data is transmitted even if one part of the system is temporarily unavailable. This service supports various messaging patterns, such as queues for point-to-point communication and topics for publish-subscribe scenarios. With features like message durability, automatic scaling, and integration with other Azure services, Azure Service Bus helps developers build robust and scalable applications.