Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.
shake hands with (someone)
to shake the hand of someone to greet them
I shook hands with my neighbor when I first met him.
List of common idioms, their meanings and examples of their usage in sentences
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.