An indefinite adjective is an adjective formed from an indefinite pronoun.  The most common indefinite pronouns are: all, any, anyone, anything, each, everybody, everyone, everything, few, many, nobody, none, one, several, some, somebody, and someone.

When used as adjectives, these are known as "indefinite adjectives".

Examples:

There are several in the safe room. (indefinite pronoun)
There are several people in the safe room. (indefinite adjective)
I have seen some in the cupboard. (indefinite pronoun)
I have seen some cartridges in the cupboard. (indefinite adjective)
 
There are only a few deer left, and we need to tag each one.