Question

what do You mean by lateral shift or lateral displacement

Answer 1

Lateral Displacement. The perpendicular distance between the incident ray and the emergent ray is defined as lateral shift. This shiftdepends upon the angle of incidence, the angle of refraction and the thickness of the medium.
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Answer 2

when a light ray gets refracted through a glass slab then we observe that the refracted ray is parallel to the incident ray but is displaced a little
this displacement between the refracted and the incident ray is called lateral displacement