An indefinite adjective is similar to an indefinite pronoun, except that it modifies a noun, pronoun, or noun phrase. An indefinite adjective tells you some information about a noun without being exact in its description.

Common indefinite adjectives are the words a lot of, all, another, any, both, each, either, enough, few, less, little, lots of, many, more, most, much, neither, other, several, and some. All tells you every single one, but doesn’t tell you exactly how many this is. Enough indicates that you have the required amount. Many means quite a few, but doesn’t tell you exactly how many. Examine the following sentences:

Many people believe that corporations are under-taxed.

The indefinite adjective "many" modifies the noun "people" and the noun phrase "many people" is the subject of the sentence.

I will send you any mail that arrives after you have moved to Sudbury.

The indefinite adjective "any" modifies the noun "mail" and the noun phrase "any mail" is the direct object of the compound verb "will send."

They found a few goldfish floating belly up in the swan pound.

In this example the indefinite adjective modifies the noun "goldfish" and the noun phrase is the direct object of the verb "found":

The title of Kelly's favourite game is "All Dogs Go to Heaven."

Here the indefinite pronoun "all" modifies "dogs" and the full title is a subject complement.