The saying “once in a
blue moon” means “very rarely; very infrequently”.
For Example:
My brother lives in
France, so I only see him once in a blue
moon.
This is the Idiom #6 in the List of 100 commonly used Idioms in everyday English (Top 100 famous Idioms). By introducing this list of notable idioms to English learners and ESL students as you, we believe that your English will sound more like a native and you can easily understand what native speakers are saying. Please like and share this list with your friends if you think it is helpful - the full list is here.