Shape constancy refers to the tendency to perceive objects as being the same shape even though the shapes of their retinal images may differ when the objects are viewed from different
positions.
Shape constancy is when the perceived shape of an object is unaffected by changes in its retinal image.
Moreover, Shape constancy is the ability to perceive the shape of an object despite the movement or rotation of the object, the objects are perceived to have a given shape regardless of the angle from which they are viewed.