An idiom is a group of words, or in other words, a phrase that has a meaning other than its literal meaning of the words in it.
Idiom:
occur to (someone)
Meaning:
to come into someone's mind (an idea or thought)
Example:
It occurred to me that I will not be able to meet my friend on Saturday because I have to go to the airport to meet someone else.
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.