An adjective clause is a grammatically related sequence of words that includes both a subject and a predicate and functions as an adjective. Adjective clauses modify a noun or pronoun, which they usually follow. Most adjective clauses begin with a relative pronoun (that, which, who, whom, whose), but they may also begin with when, where, or why.
Sam's dream was to open a store that specialized in comic hooks. [The italicized adjective clause modifies store.]
That's the school where I went to second and third grades. [The italicized adjective clause modifies school.]
Adjective clauses can modify nouns and pronouns in all common noun positions: subject, subject complement, and object.
The photography exhibit that caused so much controversy is now at the Vought Gallery. [The adjective clause modifies the subject, exhibit.]
I have not seen the picture that caused so much controversy. [The adjective clause modifies the direct object, picture.]
I gave my neighbor, whose daughter studies art, a copy of the program guide. [The adjective clause modifies the indirect object, neighbor.]
There are several excellent reproductions in the program that I gave you. [The adjective clause modifies the object of a preposition, program.]
The best picture is a self-portrait that the artist did in 1983. [The adjective clause modifies the subject complement, self-portrait.]
The relative pronoun that often can be omitted.
The picture [that] I liked best was a portrait of the artist's mother.
(See also dependent-clause errors.)