This document discusses different types of crystalline defects including point defects, linear defects, and interfacial defects. It describes point defects as vacancies where an atom is missing from its lattice site or as self-interstitials where an atom occupies an interstitial void space. Impurities are also considered point defects when added to alloys to impart specific material properties. Linear defects called dislocations are discussed as one-dimensional defects where some atoms are misaligned around an extra half-plane of atoms. Dislocations can be in the form of an edge dislocation along the end of the extra half-plane or a screw dislocation involving a shear distortion of the crystal structure.