Glossaryidioms
Idioms are phrases that mean more than their words put together. If you take them word for word, they might not make much sense! Idioms are a little like puzzles: try imagining a picture or a situation that the phrase suggests, and guess at the meaning from there.
For example, when someone says something was "a flash in the pan", they are referring to something that looked like it would be a big success, but did not work out.
From: http://www.worldalmanacforkids.com/WAKI-ViewArticle.aspx?pin=wak-014007&article_id=289&chapter_id=6&chapter_title=Language&article_title=Idioms