A definite article is a word used to specify a particular noun that is already known to the reader or listener. In English, the definite article is "the." It indicates that the noun it modifies is unique or has been previously mentioned, such as in the phrase "the book" where it refers to a specific book rather than any book. Definite articles help clarify communication by signaling that the speaker is referring to something specific. For example, in the sentence "I saw the dog in the park," "the" indicates a particular dog that both the speaker and listener are familiar with, rather than any dog.