What do you call phrases that cannot be translated literally but are understood by native speakers?

The term for phrases that cannot be translated literally but are understood by native speakers is idioms. Idioms are unique constructions where the meaning of the phrase as a whole differs from the meanings of its individual words. For example, the phrase "kick the bucket" in idiomatic usage means to die, which does not correlate with the literal meanings of the words involved. Native speakers understand these phrases intuitively because they are commonly used in the language and culture, making them an integral part of everyday communication.

In contrast, metaphors involve a direct comparison between two unlike things to create meaning, but they do not necessarily fall into a category where their meanings are obscure to non-native speakers. Expressions can encompass a broad range of phrases and are not restricted to those that defy literal translation. Slang refers to informal language that varies by region and group but does not primarily focus on phrases with non-literal meanings. Thus, idioms are the most accurate descriptor for phrases that hold meanings beyond their literal interpretations.