A fad or craze was a cultural practice that was known for catching on quickly, but ultimately being short-lived.
In 2259, Pelia told La'an Noonien-Singh that she had once lived in a bunker in Vermont on the off chance that the Earth's "no money, socialist utopia thing" was a fad. (SNW: "Tomorrow and Tomorrow and Tomorrow")
In 2364, Beverly Crusher described the late 20th century practice of cryonics as a fad. Later, after being newly awakened from cryonic freezing, Ralph Offenhouse expressed his delight at having been frozen and revived successfully, saying his stock in the company must have split a dozen times since he was frozen. Data corrected him, reiterating that it was a fad and adding that it didn't last far beyond the mid 21st century. (TNG: "The Neutral Zone")
In 2368, after Wesley Crusher expressed his concerns about the crew of USS Enterprise-D spending so much time playing the Ktarian game, Robin Lefler assured him it was a fad and would probably die out in about a week. (TNG: "The Game")
Tom Paris introduced at least two crazes that spread among the crew of USS Voyager as of 2375; yo-yos and sheer lunacy. (VOY: "Think Tank")