body-parser is a middleware for parsing incoming request bodies in Node.js, available under the npm registry. It extracts the entire body portion of an incoming request stream and exposes it on req.body. It handles JSON, raw text, URL-encoded, and multipart/form-data formats, based on the Content-Type header. Widely used in Express.js applications, body-parser simplifies data handling by transforming request bodies into easily accessible JavaScript objects for further processing.