What is an idiom? It’s an expression or phrase that may be difficult to understand because it doesn’t mean the same thing that its individual words mean.
Idioms are very common in English, especially in casual conversations, but even in formal speeches and writing. Learning some of the most common or confusing ones is worth the effort.
It not only will help you understand a conversation, but also gives a much better sense of the feelings and values people are expressing. Idioms add color (and sometimes a little mystery!) to English.
Some English idioms are based on the experience of generations, and may refer to cultural conditions that no longer exist. For example, we might tell an impatient friend to “hold your horses!” (control your enthusiasm).
We say that someone needs to “bite the bullet” when they must do something unpleasant. (It refers to giving soldiers a bullet to clamp between the teeth to avoid screaming when facing an operation without anesthesia.)
Some idioms come
from sports: “It’s in the ballpark” (in the same general range, approximately
the same)or “Give me a ballpark figure” (an estimate), both now used mostly in
business discussions. See Sports Idioms.
Some idioms come from observing animals. ”Let sleeping dogs lie” means not to disturb a situation that is currently calm but has the potential for trouble. Other idioms refer to our bodies or daily activities-- almost any shared cultural experience. Many began as metaphors, but they have become so common we often do not think about the original picture they suggested.
One very common class of idioms is phrasal verbs-- verbs with an added particle at the end, like get up, figure out, or run out of. The meaning of the phrase may be obvious-- or not.
English has innumerable idioms and proverbial expressions, more than could be put on any list. Check a good English dictionary for expressions you may not find on a list. Most dictionaries list phrasal verbs and other common idioms under the verb or other important first word of the expression.
One free online dictionary that is good for contemporary English expressions is Longman's Dictionary of Contemporary English. Some common phrases can be found with the Search box, but many more are not listed there but can be found by using “Browse the Dictionary.” (You choose the letter of the alphabet, and then the page with the verb or other “headword” that starts the idiom.)
See also these Voice of America readings on idioms with sound recordings and lots of examples.
So, what is an idiom? It's a not-so-obvious expression or phrase well-worth learning, because it's basic to the way English speakers think.