In syntax, a constituent is a word or group of words that functions as a unit within a sentence. Constituents are the internal structures of sentences.
Examples of constituents
The subject, who or what the sentence is about
The predicate, which adds detail or information to the subject
A noun phrase, such as "The man with the old brown shoes"
A prepositional phrase, such as "with the old brown shoes"
An adjective phrase
An adverb phrase