When Standalone (also referred as 'Untethered') is referenced in Virtual Reality - it simply means headsets that are free from wires, so don't require being physically attach to a PC. The Oculus Quest and Quest 2 are perfect examples of standalone headsets, as is the DecaGear 1. Examples of a tethered headset (attached to a PC), would be the Valve Index and Oculus Rift S. Standalone headsets are often preferred to the tethered kind because it gives the user more freedom to move in their environment without the restriction of wires.