An adjective describes a noun. A noun is a person, place or thing. Note, a thing can be concrete (something you can touch e.g., the object "book") or abstract (something you cannot touch e.g. the feeling "surprise!").Originally Posted by Unregistered
Adjectives answer the question What kind of?
EX: a black cat. (What kind of cat?)
EX: a swimming pool. (What kind of pool?)
EX: a rotten apple. (What kind of apple?)
Adjectives don't have to be a single word, and they don't have to come before the noun:
EX: a man who is tall. (What kind of man?)
EX: a house that is big. (What kind of house?)
Adjectives can occur at the end of a sentence, away from their noun:
EX: He is nice.
EX: She is asleep.
With the verb To Be (is, am, was, were, are, etc.), the adjective occurs after the verb, and reaches back across the verb to modify the subject. That kind of structure is called a linking structure, and To Be is called a linking verb. The adjective is called a subject complement, specifically a predicate adjective.