Bandwagon means joining a popular activity, movement, or cause mainly because many other people are doing it, rather than because you've thought carefully about it yourself.

When your classmates suddenly all start collecting the same trading cards or wearing the same style of sneakers, they've “jumped on the bandwagon.” If a sports team starts winning and suddenly everyone claims they've always been fans, those newcomers are bandwagon fans. The phrase often carries a hint of criticism: it suggests people are following the crowd without really thinking for themselves.

There's nothing wrong with liking popular things, of course. But bandwagon behavior means choosing something mainly because it's popular, not because you genuinely care about it. A true fan supports their team through losing seasons. A bandwagon fan only shows up when winning makes it easy and fun. When someone accuses you of “jumping on the bandwagon,” they're suggesting you're following the crowd instead of making your own choice.