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Cheap heat is getting booed by people in the building for a single segment, usually for shit that people at home don't care about and won't want to see the guy lose for like the classic sports team insulting.
Go away heat is where no one wants to see the heel lose, but rather they don't buy the PPV or will stop watching. Usually the smarks who use this terminology are the ones who will watch anyway so won't actually have go away heat, but go away heat absolutely exists or WWE wouldn't have run off half their fanbase.
Not understanding terms doesn't mean they don't exist.