has-been. The word "has-been" means someone who is no longer popular.
has 和 been放一起就是过气的人,过时的东西。
This guest star used to be famous and popular, but now she's just a has-been.
comeback 就是东山再起,咸鱼翻身的意思.
If this singer makes a comeback, she will regain her popularity!
So,第一:人气叫 popularity; 第二:过气、过时的人或物是 a has-been; 第三:东山再起是 a comeback.