(1) Anatomically, the region in the retina that is not sensitive to light and where the optic nerve and blood vessels pass through
(2) The obscuration in the visual field as caused by the lack of photoreceptors on the optic disc
Most vertebrates, including humans, have a blind spot in their vision field. Cephalopods, in contrast, are the animals that do not have a blind spot.
A blind spot is a normal phenomenon first to be documented by Edme Mariotte in 1660s. A blind spot in the vision though does not create a "hole" in the vision field but a continuous background filled in by the brain. Thus, there could be some details or information that may go unnoticed due to blind spot.