An idiom is a type of phrase or expression that has a meaning that can't be deciphered by defining the individual words.
Idiom:
sweep (someone) off his or her feet
Meaning:
to overcome someone with strong feelings
Example:
We were swept off our feet by the excitement of the ceremony.
List of common idioms, their meanings and examples of their usage in sentences
An expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements or in its grammatically atypical use of words.