In the following question, out of the given four alternatives, select the alternative which best expresses the meaning of the Idiom/Phrase.

Once in a blue moon

Rarely

The idiom "once in a blue moon" means rarely. It is used to describe something that happens very infrequently or seldom. The phrase is thought to have originated from the fact that a blue moon is a second full moon in a month. This happens very rarely, about once every 32 months.

The other alternatives are not correct.

• Once in a day: This is not the same as once in a blue moon.
• Frequently: This is the opposite of once in a blue moon.
• Once a week: This is not as rare as once in a blue moon.