Fleeting trend (3)
I believe the answer is:
fad
'fleeting trend' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fad that I've seen before include "Craze; idiosyncrasy" , "Temporary vogue or craze" , "Passionate interest" , "A craze or current vogue" , "Short-lived craze" .)