An idiom is a phrase or expression that has a figurative meaning different from its literal meaning. Idioms are often unique to a particular language or culture and can be challenging for non-native speakers to understand because their meanings are not easily deduced from the individual words. For example, the idiom "kick the bucket" means to die, which is not something you would gather just by looking at the individual words in the phrase.
The word "idiom" originates from the Greek word "idios," which means "one's own" or "private." It evolved into Latin as "idioma," meaning "a peculiar phrase or expression."