A term usually used in photography. It refers to the image angle that a particular lens covers. The terms hFoV (horizontal) and vFoV are sometimes used to distinguish image dimensions.
The shorter the focal length of a lens, the wider it's field of view. For example, a 50mm lens might have 45 degrees FoV, while a 16mm fisheye may be around 130 degrees FoV.
The term is also used in 3D Graphics to describe the image area encompassed by a virtual camera.