as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
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describe the meaning of the phrase "once in a blue moon".
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the phrase "once in a blue moon" is an idiom that means something that does not happen very often, or something that is rare. it is derived from the fact that a blue moon - the second full moon in a calendar month - is a rare occurrence.
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