Persistence of vision is the ability of human eyes to retain an image of what they have just seen for a short period of time after the object has disappeared from sight. A person can "see" a light for a second or two after the light has been turned off.
If an electric light bulb is placed behind an electric fan moving at high speed, the light seems to shine continuously although the fan blades are covering it for short intervals. This persistence of vision explains why still pictures shown rapidly appear to move. Motion pictures are actually numerous still pictures shown so rapidly that they seem to blend into one continuous moving picture.
