Defect chemistry is a field of study within materials science and solid-state chemistry concerned with the nature, concentration, and behavior of structural imperfections (defects) in crystalline and non-crystalline solids. It investigates the thermodynamic and kinetic aspects of defect formation, their charge states, interactions, and transport, and critically examines how these defects profoundly influence the physical, chemical, electrical, and mechanical properties of materials, providing principles for defect engineering to optimize material performance.