Responsive Web Design (RWD) is a Web development concept focusing on making sites look and behave optimally on all personal computing devices, from desktop to mobile. [1]

The viewport meta tag is part of what makes RWD possible. [2] The viewport meta tag does not relate to PiP in any way that I can imagine.

[1]: https://developer.mozilla.org/en-US/docs/Glossary/Responsive...

[2]: https://developer.mozilla.org/en-US/docs/Mozilla/Mobile/View...