It's hot until it's not (3)
I believe the answer is:
fad
'it's hot until it's not' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for fad that I've seen before include "Particular like or dislike, or a craze" , "Personal whim" , "Temporary vogue or craze" , "Passing craze or peculiar notion" , "A craze, usually passing" .)