idiom!

"once in a blue moon" means rarely; occasionally

Bob: Do you ever go fishing?
Luther: Once in a blue moon.

Jenny: Do you drink much alcohol?
Flemy: I did when I was in college, but now only once in a blue moon.

Frank: What do you think of the school principal?
Eliza: I don't have much of an opinion about him. I only see him once in a blue moon. He's almost always in his office.


Use it wisely!!