In everyday speech, a phrase may refer to any group of words. In linguistics, a phrase is a group of words (or sometimes a single word) that form a constituent and so function as a single unit in the syntax of a sentence. A phrase is lower on the grammatical hierarchy than a clause.

Examine the following sentence:

The words in bold form a phrase; together they act like a noun. This phrase can be further broken down; a prepositional phrase functioning as an adjective can be identified:

Further, a smaller prepositional phrase can be identified inside this greater prepositional phrase:

And within the greater prepositional phrase, one can identify a noun phrase:

Phrases can be identified by constituency tests such as proform substitution (=replacement). For instance, the prepositional phrase at the end of the street could be replaced by an adjective such as nearby: the nearby house or even the house nearby. The end of the street could also be replaced by another noun phrase, such as the crossroads to produce the house at the crossroads.