An edge dislocation is a linear crystallographic defect formed by an extra half-plane of atoms inserted into an otherwise perfect crystal lattice. The boundary line terminating this extra half-plane defines the dislocation line, around which compressive stress exists above the slip plane and tensile stress exists below it. Under applied shear stress, the dislocation glides along the slip plane one atomic spacing at a time, mediating plastic deformation at stresses orders of magnitude lower than theoretical lattice shearing.