What is middleware in Node.js?

Middleware in Node.js refers to functions that sit between the incoming request and the final request handler. Each middleware receives the request and response objects, and a next function to pass control to the next middleware. They are used for tasks such as logging, authentication, parsing request bodies, handling errors, and modifying request/response objects. In Express, middleware can be applied globally, to specific routes, or to route groups. For example, app.use(express.json()) parses JSON bodies for all routes. Middleware can be chained, and the order of registration determines the execution order.