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/881282079/The-Art-of-Choosing-a-Winning-Technique-for-Online-Casino-Slots-182136

The suggestion of "sizzling" and "chilly" slots refers to machines that appear to pay out more often than not or in no way, though those traits are lastly random.