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.
Idiom:
hold on to (someone or something)
Meaning:
to continue to hold or keep something, to hold someone or something tightly
Example:
You should hold on to your bag when you are in the bus or someone may steal it.
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.