Can you please ELI5 tmux?

I am fairly familiar with Linux, I've been using different distros for some years now and have done some config editing here and there. I am also a web developer and use the terminal quite a lot and so I always stumble on people's recommendation to use tmux and how good it is, but I never really understood what it does and, in layman's terms, how can it be useful and for what use cases.

Can you guys please enlight me a bit on this?

Thank you.

Edit: if my phrasing is a bit awkward or confusing I apologize since I am not an English native speaker. (Maybe that's why I never fully grasped what tmux is from other explanations xD)

Edite: Ok, just to clarify, my original struggle was to understand what made tmux different from using some terminal app and just split the screen xD