An idiom is a group of words, or in other words, a phrase that has a meaning different from the literal meaning of the words in it.
get the lowdown on (someone or something)
to receive the full story about someone or something
I met a friend for coffee to get the lowdown on our friend who is getting married.
List of common idioms, their meanings and examples of their usage in sentences
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.