Surface defects (2-D) are the boundary between two orderly regions of a crystal.  In other words, they are separate regions having different crystallographic orientations.

• the simplest form composed of parallel array of edge dislocations , tilt boundary
• twin boundaries are a particular type of boundary where one portion of the lattice is a mirror image of the other; the mirror is the twinning plane growth

                                                                Twin boundary 2D