An idiom is an expression whose meaning is not clear from the meaning of its words. In other words, idioms have meanings that can not be figured out by looking the words up in a dictionary. They have meanings that are understood by people who speak that language, but are very hard to understand for people who do not speak the language.
To see how idioms can be confusing read this:
In England potato chips are called "Crisps". In Canada they are called "Chips". In England "Chips" mean French Fried Potatoes, but in Canada we call them "Fries". Small Fry in Canada means a child or kid but if you look up "kid" in the dictionary, you find out it actually means a baby Goat. "To Get Someone's Goat" in Canada means to "Bug" them (bother them) and on and on it goes.
Idioms can be very confusing to people who are learning a language. The pictures on this web site are of the literal meaning of the idiom, not the actual meaning in common use. If you want to see the actual meaning of the idiom you can use the letter menu above and click on the idiom you want to see or look below.