Linux is one option for the core, central part of how a computer works, called a 'kernel'. All programs talk to Linux, which talks to the physical computer.

Windows has its own version of that kernel, Mac has another.

Linux is special because it's free for people to use, change, and check what it's doing.

There's a lot of programs built to work with Linux: together they are what you use to use your computer. Like, Windows is actually lots of smaller programs working together, and Mac OS is lots of smaller programs working together. Most people say 'Linux' meaning all these programs running together, with Linux at the core.

In other words, Linux is a system that runs on your computer, so you can run the programs you want (like Emacs, or Inkscape) on top of that.