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.
Idiom:
fall off
Meaning:
to decrease
Example:
The number of tourists to the island is falling off.
List of common idioms, their meanings and examples of their usage in sentences
Idioms are phrases which cannot be understood simply by looking at the meaning of the individual words in the phrase.