An idiom is a type of phrase or expression that has a meaning that can't be deciphered by defining the individual words.
Idiom:
stick out like a sore thumb
Meaning:
to be obvious and visible
Example:
The woman sticks out like a sore thumb when she wears her red hat.
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.