A blind spot is an obscuration of the visual field. More specifically, the eye's blind spot is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells.
These photoreceptor cells are on the optic disc of the retina where the optic nerve passes through. The brain fills in information based on surrounding detail and information from the other eye so the blind spot is normally not perceived.
There is a way you can experience for yourself though. A person can look at the letters "R" and "L" about two inches apart on a screen.
These stand for Right and Left and are on the corresponding side. The person closes one of their eyes and focuses the open one on the same side's letter (e.g. if they close their right eye, they focus their left eye on the "L").
They then place their face about 6 inches away from the screen and move it forward or backward until the other letter disappears. When that happens, the person has just experienced their blindspot.