Middleware is software that provides common services and capabilities to applications outside of what's offered by the operating system. It acts as an intermediary layer between the application and the underlying infrastructure, handling tasks such as authentication, logging, data transformation, and communication between distributed components. Middleware simplifies the development process by providing reusable functionalities that can be integrated into various applications. Examples of middleware include web servers, application servers, message brokers, and API gateways. Middleware is essential for enabling interoperability, scalability, and maintainability in complex software systems.