Thermosetting plastics are synthetic materials that strengthen during being heated, but may get damaged when being tried to molded again. Thermoplastics are different. They can be remelted back into liquids and can be remolded also.
Ex for thermosetting: epoxy resin(m-seal), melamine, urea formaldehyde etc.
Ex for thermoplastics: polythene, polypropylene, polystyrene etc.