Shape memory polymers are polymers that can be deformed from an original shape to a temporary shape when exposed to an external stimulus like heat or light, and then returned to their original shape upon removal of that stimulus. The document discusses the history and chemistry behind shape memory polymers, how they are activated by heat, light, electricity or other means, and their applications in areas like medical devices and textiles. It also notes limitations like transition limits and temperature ranges that need further research to expand shape memory polymer capabilities and applications.