Middleware is a framework of hooks into Django's request/response processing. It's a light, low-level plugin system for globally altering Django's input or output.
Each middleware component is responsible for doing some specific function. For example, Django includes a middleware component, AuthenticationMiddleware, that associates users with requests using sessions.
This document explains how middleware works, how you activate middleware, and how to write your own middleware. Django ships with some built-in middleware you can use right out of the box. See Available middleware later in this chapter.