An idiom is a group of words, or in other words, a phrase that has a meaning other than its literal meaning of the words in it.
(one's) chickens have come home to roost
one's words or actions have come back to cause trouble for someone
The girl's chickens have come home to roost and now she must take responsibility for her actions.
List of common idioms, their meanings and examples of their usage in sentences
Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.