Which of the following best describes an idiom?

An idiom is best described as a group of words that convey a specific meaning that is different from the individual meanings of the words themselves. For example, the phrase "kick the bucket" is an idiom for dying, rather than referring to the literal action of kicking a physical bucket. This non-literal interpretation is what characterizes idioms, allowing them to enrich language by providing colorful expressions that often reflect cultural nuances.

The other descriptions do not encapsulate the essence of an idiom. A literal phrase with a clear meaning does not account for the figurative nature of idioms. A common noun used in literature pertains to a specific part of speech and does not relate to the idiomatic expressions we are considering. Similarly, while some idioms may be widely understood, not all expressions are universally recognized, making the last option inaccurate. Thus, the choice highlighting a group of words with a specific, non-literal meaning accurately defines an idiom.