Adjective Clause

They provide additional information about the noun or pronoun and are introduced by relative pronouns (who, whom, whose, which, or that) or relative adverbs (when, where, or why).

Subsequent are some examples of adjectival clauses:

The car, which was parked outside, belongs to my neighbor. (In this sentence, "which was parked outside" is an adjectival clause that modifies the noun "car". It provides additional information about the car, and is introduced by the relative pronoun "which".)

The woman who is singing has a beautiful voice. ("Who is singing" is an adjectival clause that modifies the noun "woman". It provides additional information about the woman, and is introduced by the relative pronoun "who".)

The book, whose cover is torn, is still readable. ("Whose cover is torn" is an adjectival clause that modifies the noun "book". It provides additional information about the book, and is introduced by the relative pronoun "whose".)

The reason why he left is unclear. ("Why he left" is an adjectival clause that modifies the noun "reason". It provides additional information about the reason, and is introduced by the relative adverb "why".)

Adjectival clauses can be restrictive (essential) or nonrestrictive (nonessential). Restrictive clauses are necessary to the meaning of the sentence and are not set off by commas. Nonrestrictive clauses are not necessary to the meaning of the sentence and are set off by commas.