# Concepts

- [What is BabylonJS?](https://www.xrdev.app/mixed-reality-docs/webxr-lessons/babylon.js/concepts/what-is-babylonjs.md): Overview of WebXR and BabylonJS features.
- [What is a scene?](https://www.xrdev.app/mixed-reality-docs/webxr-lessons/babylon.js/concepts/what-is-a-scene.md)
- [What is Playground?](https://www.xrdev.app/mixed-reality-docs/webxr-lessons/babylon.js/concepts/what-is-playground.md)