Eyebox
An eyebox is an area in physical space from which an entire image produced by a display can be seen.[1] In other words, it is a volume where an eye receives a full and complete view of a displayed image.
The eyebox of point based displays is huge.
The eyebox of ray based displays, such as projectors, is typically small, because the rays only travel in one direction or a narrow ray cone.
Point based displays are those used in standard VR headsets like the Oculus Rift.