Ideally, everything will work seamlessly on a website, without the need for any additional steps to be taken. You take your source files, drop them on a web server, and voilà : a site. However, this isn't always the case. For example, with React, we need to run npm run build to generate an output distribution directory for our project. We might also have other types of non-source files, such as SASS or TypeScript, which need to be converted into native file formats that the browser can understand.
So, what is a module? There's the concept of modular programming, which takes large programs and separates them by concern and encapsulation (scope) into smaller, contained chunks called modules. The ideas behind modular programming are many: scope, abstraction, logical design, testing, and debugging. Similarly, a bundle is a chunk of code that a browser can easily use, usually constructed from one or more modules.
Now here's the fun part...