Trend, craze (3)
I believe the answer is:
fad
I believe this is a double definition.
'trend' is the first definition.
(a fad is a brief craze or fashion)
'craze' is the second definition.
(I know that craze can be written as fad)
(Other definitions for fad that I've seen before include "Passing craze or peculiar notion" , "A passing fancy or fashion" , "Affectation" , "A craze or current vogue" , "Short-lived craze" .)