The concept of "hot" and "cold" slots refers to machines that seem to pay out frequently or not at all
https://www.scribd.com/document/879860139/Celebrating-Traditional-Slots-The-Ageless-Favorites-of-Gambling-Establishments-193919
The idea of "scorching" and "cold" slots refers to machines that seem to be to pay out incessantly or never, even though these tendencies are not directly random.