Field of view or FOV is the observable visual extent of a view. It is usually measured in degrees.
Virtual reality headsets typically have a field of view of at least 90 degrees. The higher an HMD's FOV is, the further the virtual world will extend to your edge of vision.
The field of view of a normal computer screen is approximately the center third of the vision. Either desktop or laptop.
The field of view of a head mounted display needs to be higher than a world-fixed computer to be comfortable. This is because when you turn your head with a headset, the content stays fixed in the world and gets cut off at the sides in your periphery. This is highly noticable with the Magic leap 1 and Hololens 1.