Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.
Idiom:
a must have
Meaning:
something that you must have
Example:
The new computer screens are a must have for computer users.
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.