An "idiom" is a phrase whose meaning is different from the meaning of the words themselves. In other words, if you looked up each word of an idiom in the dictionary, the expression wouldn't make any sense — or at least not mean what the speaker intended it to mean.
Consider the expression “it's raining cats and dogs." This common idiom means it's raining very hard. If you think about the meaning of the individual words in the phrase, though, you'd expect to see cats and dogs falling from the sky!
English idioms, easily understood by native speakers, can nonetheless greatly confuse non-English speakers. Scholars estimate that the English language has more than 25,000 idioms!
Why do we use idioms so often, especially if they might confuse our listeners? As you think about common idioms, you'll realize they allow us to express thoughts and emotions that other words can't communicate as clearly or cleverly. Idioms feature imagery and symbolism that help us to express ourselves more effectively.
Though you may not realize it, you probably already know all sorts of idioms. Let's take a closer look at the meaning of the phrase “a dime a dozen."
This idiom means something is extremely common, inexpensive or available anywhere. Although it doesn't literally mean you can purchase something for less than one cent, it does effectively convey the idea that something is inexpensive or easily obtainable.
Let's say you are headed to the beach with a friend. On the way, your friend realizes she forgot to pack a beach towel.
Since many beach shops sell inexpensive towels, you might say, “Don't worry. Beach towels are a dime a dozen where we're going!" Because your friend understands the idiom, she now knows there will be plenty of places to buy a towel at a very affordable price near the beach.