A: An idiom is some phrase or sentence that is considered part of a dialect of a culture that people from another culture or who speak a different language would have trouble figuring out.
Examples:
"We beat them"
Literally, that would mean "We caused bodily harm," but when referring to say a football game it means "We won the game."
"Our breakup tore me to pieces"
We're talking about a relationship and feelings, not physically being torn apart.
Given these are pretty bad examples (hey, it's 12:15am!)...
Idioms are used a lot more than one could imagine. The way to think about it is really "Would someone from a completely different culture who uses a completely different language understand what I'm trying to communicate?" If the answer is no, it's an idiom. I hope I was of some help. Try to come up with your own. Perhaps they'll be better than mine.
