The document discusses smart materials, which are materials that respond to environmental stimuli like temperature, pressure, or light. Smart materials have properties of sensing their environment, acting in response, and potentially self-healing. They are classified into groups like piezoelectric, shape memory alloys, and quantum tunnelling composites. Some applications of smart materials include aircraft, medical devices, smart glass, and more. They offer benefits like compactness and safety mechanisms but also have costs like complexity and limited bandwidth.