In an injection molding tool, the melt channel between cylinder and cold runner / cavity is called hot runner.
The difference from a cold runner is that the hot runner has at least one heater band to keep the hot runner at temperature.
The melt inside the hot runner stays fluid during the complete cycle and will be used directly for the next shot.
No waste is produced.
Hot runners are used to save material or to avoid weld lines (sequential injection).
This glossary of plastic industry is provided by PLEXPERT Canada Inc.