Microsoft Message Queuing, or MSMQ, is a messaging protocol that allows applications running on separate servers to communicate with each other. It enables the sending and receiving of messages between applications in a reliable and asynchronous manner, ensuring that messages are not lost even if the receiving application is temporarily unavailable. MSMQ supports various messaging patterns, such as point-to-point and publish-subscribe, making it versatile for different application needs. It is commonly used in enterprise environments to facilitate communication between distributed systems, ensuring that data is transmitted securely and efficiently across networks.