Virtual Reality(VR) is technology that builds the virtual world in 3-dimension(3D) for computer simulation, and must use visual devices to respond and access the system.
Augmented Reality(AR) is similar to VR technology that builds virtual objects and displays them on supporting devices, that means AR supports by creating virtual objects in real environments.

Both VR and AR are used for meeting and training through simulations popularly but those technologies are not yet the end. Mixed Reality(MR) combines the virtual world with the real world together which interact in real-time.
And the last one Extended Reality(XR) that was updated on 10 December 2020, XR refers to all real and virtual environments that have interaction between human and machine. XR consists of all technologies VR, AR, and MR, some people will define XR by X can represent with any letters.

Reference :
https://www.mmthailand.com/xr-technologies-possibilities/
https://www.keencollective.co.th/blog/reality-%E0%B8%97%E0%B8%B5%E0%B9%88%E0%B9%81%E0%B8%95%E0%B8%81%E0%B8%95%E0%B9%88%E0%B8%B2%E0%B8%87%E0%B8%82%E0%B8%AD%E0%B8%87-ar-vr-mr-%E0%B9%81%E0%B8%A5%E0%B8%B0-xr/