What defines a phrase in grammatical terms?

A phrase is defined as a combination of words that lacks either a subject or a verb, making the third option the correct choice. This definition captures the essence of what a phrase is in grammar: it is not a complete sentence and does not convey a complete thought, as it does not contain both necessary components. For instance, "under the bridge" is a phrase because it lacks a subject and a verb but conveys an idea about location.

In contrast, the first option describes a complete sentence or a clause rather than a phrase since it suggests the provision of a complete thought. The second option defines a clause, not a phrase, as it specifies the presence of both a subject and a verb. The fourth option refers to a specific type of sentence, a command, which is also not related to the definition of a phrase. Understanding these distinctions is important for grasping the structure of complex sentences and the roles that phrases play within them.