the word or group of words that completes the sense of the subject when the sentence contains a copulative verb such as to be. It is not the same as a direct object, and is placed in the subjective or nominative case.
A Subject Complement occurs with a copular verb. It provides additional information about the Subject. For example, Alan is an artist. In this example the noun phrase an artist is the Subject Complement and it provides more information about Alan.
The subject complement is the word (with any accompanying phrase) or clause that follows a linking verb and complements, or completes, the subject of the sentence by either (1) renaming it or (2) describing it. The former, a renaming noun (or sometimes a pronoun), is technically called a predicate noun or predicate nominative (or in some cases, a predicate pronoun). The latter, a describing adjective, is called a predicate adjective.