Webpack is a module bundler for modern JavaScript applications. It takes modules with dependencies and generates static assets representing those modules. Webpack provides a unified approach to bundling, transforming, and loading all of your project's static assets. It allows you to write modular code and bundle it together into small packages to optimize load time. Webpack also provides plugins and loaders that allow you to preprocess, minify, and transpile your code so it can run in different environments.