In grammar, a phrase is a group of words that functions as a single unit in the syntax of a sentence.

For example the house at the end of the street (example 1) is a phrase. It acts like a noun. It contains the phrase at the end of the street (example 2), a prepositional phrase which acts like an adjective. Example 2 could be replaced by white, to make the phrase the white house. Examples 1 and 2 contain the phrase the end of the street (example 3) which acts like a noun. It could be replaced by the cross-roads to give the house at the cross-roads.

Most phrases have a or central word which defines the type of phrase. This word is called the head of the phrase. In English the head is often the first word of the phrase. Some phrases, however, can be headless. For example, the rich is a noun phrase composed of a determiner and an adjective, but no noun.

Phrases may be classified by the type of head they take

• Prepositional phrase (PP) with a preposition as head (e.g. in love, over the rainbow). Languages that use postpositions instead have postpositional phrases. The two types are sometimes commonly referred to as adpositional phrases.
• Noun phrase (NP) with a noun as head (e.g. the black cat, a cat on the mat)
• Verb phrase (VP) with a verb as head (e.g. eat cheese, jump up and down)
• Adjectival phrase with an adjective as head (e.g. full of toys)
• Adverbial phrase with adverb as head (e.g. very carefully)

Formal definition

A phrase is a syntactic structure which has syntactic properties derived from its head.

Complexity

A complex phrase consists of several words, whereas a simple phrase consists of only one word. This terminology is especially often used with verb phrases:

• simple past and present are simple phrases, which require just one verb
• complex verb have one or two aspects added, hence require additional two or three words

"Complex", which is phrase-level, is often confused with "compound", which is word-level. However, there are certain phenomena that formally seem to be phrases but semantically are more like compounds, like "women's magazines", which has the form of a possessive noun phrase, but which refers (just like a compound) to one specific lexeme (i.e. a magazine for women and not some magazine owned by a woman).

Semiotic approaches to the concept of "phrase"

In more semiotic approaches to language, such as the more cognitivist versions of construction grammar, a phrasal structure is not only a certain formal combination of word types whose features are inherited from the head. Here each phrasal structure also expresses some type of conceptual content, be it specific or abstract.