Per-eye resolution
Short definition
Per-eye resolution is the number of pixels a virtual reality headset shows to each eye, which, together with the optics and field of view, determines how sharp the image is.
In plain language
Because the display is very close to the eyes and the image is magnified by the lenses, low resolution shows up as a grid or grainy image. A more useful measure for comparing devices is the density in pixels per degree of field of view. In 360° video, sharpness also depends on the resolution at which the video was filmed, since those pixels are spread across the whole sphere.