An idiom is defined as - a group of words in a fixed order that has a particular meaning that is different from the meanings of each word on its own.
out of gas
to have no gas in a vehicle, to be tired or exhausted
The truck was out of gas so we could not use it last night. I was out of gas so I went home and went to bed.
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.