What does a VR Ready computer mean technically?
Does an industry standard exist that specifies a VR Ready computer has to be able to render X number of triangles twice (left and right eye) at a frame rate F at a resolution R, where X, F and R are defined some industry standard?
Oculus has quite strict guidelines on what are the minimal requirements. It will not work or at least will constantly nag you if your machine isn't up to spec.
Vive has minimum specs, but they're not so orthodox in enforcing them as Oculus is.
OSVR has no such thing as far as I know - and it works almost everywhere.
That said, the stereoscopic display and rotation measurement actually isn't that costly in terms of computing power¹, the specs above are arbitrary and provided as a baseline for content makers. For example VR video can work on really old machines, provided that middleware (Oculus drivers mostly) doesn't forbid you to.
¹ positional tracking is moderately expensive in case of camera based trackers like Oculus or OSVR. Still, it mostly eats up USB bandwidth and not that much of the CPU. Vive has no such issue.