What is operating system means?

Operating system is the interface between user and computer. GUI( graphical user interface) so user can access and use the application easily they not need to worry about the background process for Example- If you want to copy a file just click copy by your mouse or ctrl+c and you ready to copy. No need to understand that how system doing all these thing.

So in short , operating system is a application which makes computer interface easy to use for user.