Answer
An idiom is an expression whose symbolic meaning is different from its literal meaning.
Step-by-step explanation:
An idiom (/ˈɪd·i·əm/) is an expression or phrase that contains specific words in a specific order; the meaning of an idiom is not connected with the definition of each word that the idiom contains. In other words, when trying to understand the meaning of an idiom, one shouldn't try to descipher the definiton of each word, because idioms are fixed expressions (that's why word order cannot be changed) that have a symbolic meaning. Below you can find some examples of idioms and its definitions:
Idiom: "go belly up"
Example: If we keep wasting our money like this, we'll go belly up. (= We'll go bankrupt)
Idiom: "rocket science"
Example: I can fix my computer, it's not rocket science. (= It's not hard to fix a computer)
Idiom: "It takes two to tango"
Example: You can't do this job on your own, it takes two to tango. (= it is necessary two people to make something work).