A fad or craze was a cultural practice that was known for being short-lived.
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")