A subject complement is a word or phrase that follows a linking verb and provides additional information about the subject of the sentence. It can be a noun, pronoun, or adjective that renames or describes the subject. For example, in the sentence "The sky is blue," the word "blue" is the subject complement that describes the subject, the sky. Subject complements are essential for completing the meaning of a sentence. They help clarify or elaborate on the subject, making the sentence more informative. In the sentence "She is a teacher," the phrase "a teacher" serves as a subject complement, identifying she as a specific role.