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" serves as the subject complement, describing 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" acts as a subject complement, identifying she as a specific role.