A style, activity, or interest that is very popular for a short period of time. (Cambridge Dictionary)
You use fad to refer to an activity or topic of interest that is very popular for a short time, but which people become bored with very quickly. (Collins Dictionary)
An intense and widely shared enthusiasm for something, especially one that is short-lived; a craze. (Oxford Dictionaries)
Is User Experience a Fad?
What Is the Most Significant Fad of All Time?