Message-oriented middleware (MOM) is a software layer that facilitates communication between different applications or services by sending messages. It allows these systems to exchange data asynchronously, meaning they do not need to be connected at the same time. This decoupling enhances flexibility and scalability in distributed environments. MOM typically uses a messaging queue to store messages until they can be processed by the receiving application. This ensures that messages are not lost, even if the recipient is temporarily unavailable. Common examples of MOM include RabbitMQ, Apache Kafka, and ActiveMQ, which help streamline communication in complex systems.