: a word or phrase preceded by the symbol # that classifies or categorizes the accompanying text (such as a tweet) You know a thing is really a thing these days when it has its own hashtag. And there it was last week, trending on Twitter alongside #cincodemayo and #happymothersday: #umpshow, which sprang up in the wake of some shockingly bad umpiring over the first six weeks of the major league season. Joe Sheehan It's also true that a popular hashtag can benefit important and worthy subjects, such as the recently kidnapped Nigerian schoolgirls. Mark Leibovich also : the symbol # as used in a hashtag