Heat treating or heat treatment is the name for a number of processes in metallurgy: All processes have in common that the piece being worked on is heated for some time, and then cooled off. This is done to change some of the properties of the workpiece. Heat treating is used for pieces of metal, for certain alloys, and for certain types of plastic. With ceramics, a form of heat treating is part of the production process, and is called sintering.
There is also a concept called hot working, but it is different.