To me, idioms are phrases or statements that don't make common sense. They are often found locally and regionally--that is, certain people from certain areas have their own kinds and sayings. Idioms are especially hard for people who are learning English because the idea or statement gives a VERY wrong impression.
Example: I once said to a college class that "I had a tiger by the tail." As an idiom, that means I had found myself in a difficult situation.
After class, a lady from India came up to speak with me.
"Mr. Lopate, how come you are not dead? Why didn't the tiger kill you for pulling its tail?"
When I got my sense of awareness back after trying not to laugh, I understood what she meant.
In India, only a foolish person would dare such a thing--and surely be dead as a result!
She didn't know the phrase was common in the U.S., and I had to explain it as an idiom.
