A fad or trend or craze is any form of collective behavior that develops within a culture, a generation or social group and which impulse is followed enthusiastically by a group of people for a finite period of time.
Fads are things or behaviors that have achieved short-lived popularity, but fade away. Fads are often seen as sudden, quick spreading, and short-lived. Fads could include diets, clothing, hairstyles, toys, and more. Some popular fads throughout history are toys such as yo-yos, hula hoops and dances such as the Macarena and the twist. More current fads might include memes, planking, and Tebowing.
Similar to habits or customs but less durable, fads often result from an activity or behavior being perceived as emotionally popular or exciting within a peer group or being deemed "cool" as often promoted by social networks A fad is said to "catch on" when the number of people adopting it begins to increase to the point of being noteworthy. Fads often fade quickly when the perception of novelty is gone.
The specific nature of the behavior associated with a fad can be of any type including unusual language usage, distinctive clothing, fad diets or frauds such as Pyramid schemes. Apart from general novelty, fads may be driven by mass marketing, emotional blackmail, peer pressure, or the desire to "be hip". Fads may also be set by popular celebrities, e.g. the highly popularizing effect of Oprah's Book Club.