A subject complement (variously called a predicative expression, predicative, predicate noun or adjective, or complement) appears in a predicate with a linking verb (also called a copula).
en.wikipedia.org The predicate can be an intransitive verb, a transitive verb followed by a direct object, a linking verb followed by a predicate nominative, etc.
en.wikipedia.org The subject and predicative nominal must be connected by a linking verb, also called a copula.
en.wikipedia.org You're missing like three words in that sentence, including a linking verb.
mashable.com While subject complements describe or modify the subject of a linking verb, object complements describe or modify nouns in the predicate, typically direct or indirect objects, or objects of adpositions.
en.wikipedia.org