Final answer:
Thermoplastics are plastics that soften when heated and become firm again when cooled. They can be reformed after repeated heating.
Step-by-step explanation:
Thermoplastics are plastics that soften when heated and become firm again when cooled. They can be reformed after repeated heating. On the other hand, thermosets are plastics that soften when heated and harden permanently. They cannot be reformed after hardening. An example of a thermoplastic is polyethylene, which can be melted and reshaped multiple times.