blue moon
The phrase "blue moon" refers to a phenomenon when there is a second full moon within a calendar month. This occurrence is relatively rare, happening about once every two or three years. Despite the name, a blue moon does not typically appear blue in color. It is more commonly used as an idiomatic expression to describe a rare or unexpected event.
English is confusing! Why do people say "Pardon my French" when they are speaking English? Because of idioms!
An idiom is a phrase or expression that usually presents a figurative, non-literal meaning attached to the phrase. Does that sound fun? It can be!
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