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to be popular; to come into fashion
to be prevalent; to spread widely (e.g. disease); to be endemic
to flourish; to thrive
今、若者の間でこのファッションが流行っている。
This fashion is currently popular among young people.
冬場はインフルエンザが流行る。
Influenza spreads during the winter season.
去年の冬はロングブーツが流行った。
Long boots were popular last winter.