1N-UNCOUNT 昙花一现的事物 You can refer to things which last for only a short time as ephemera . 昙花一现的事物 [literary]
2N-UNCOUNT [oft adjective NOUN]只在短期内有用之物;（短期内有用之物的）收藏品Ephemera is things people collect such as old postcards, posters, and bus tickets, which were only intended to last a short time when they were produced. 只在短期内有用之物;（短期内有用之物的）收藏品