What exactly is a "webpack module" in webpack's terminology?

I am a newbie to webpack and currently trying to understand basic concepts. Looking at the official docs, on the page Concepts it uses module term and gives link to read more about modules on page Modules.

So on this page we have question "What is a module" but no explicit answer to that is given. Rather, it describes modules by how they "express their dependencies":

What is a webpack Module

In contrast to Node.js modules, webpack modules can express their dependencies in a variety of ways. A few examples are:

• An ES2015 import statement

• A CommonJS require() statement

• An AMD define and require statement

• An @import statement inside of a css/sass/less file.

• An image url in a stylesheet url(...) or HTML file.

So it doesn't explicitly defines what exactly is the module and I am confused now.

Is module just a javascript file? Or is it any type of file like .css or images? Or is module some logical concept not related to physical files at all?

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