like catchphrase -
Idiom: An idiom is a common word or phrase with a culturally understood meaning that differs from what its composite words' denotations would suggest. For example, an English speaker would understand the phrase "kick the bucket" to mean "to die" – as well as to actually kick a bucket.
here's a list to start you off: http://en.wiktionary.org/wiki/Category:English_idioms
I'll start with an easy one, guess right and it's your go. It should be fairly obvious when you get it right.