Passthrough
Short definition
Passthrough is the feature of a virtual reality headset that shows, through its external cameras, a real-time image of the space around the wearer.
In plain language
It allows the real space to be seen without removing the headset, for example to find a chair or talk to someone. It is also the basis of mixed reality on devices that do not have transparent lenses. Quality varies: some devices show the outside in black and white, others in colour.