Indefinite pronouns are pronouns that do not refer to a specific person or thing. There are two types: independent and non-independent.

Independent Indefinite Pronouns

The independent indefinite pronouns are not directly related to any noun.

Nadie está en casa.

No one is at home.

¿Ya has comido todo?

Have you already eaten everything? 

Alguien ha pintado la pared.

Someone has painted the wall.

Non-independent Indefinite Pronouns

Non-independent indefinite pronouns are used with nouns and inflect according to them.

The pronoun mucho (a lot of, much, many) is inflected according to the gender and number of the noun:

The pronoun poco (a little, few) works the same way:

The pronoun demasiado (too much, too many) also inflects according to gender and number:

The pronoun alguno (some) can be used with both people and things:

The pronoun ninguno (not one, not any) is usually only used in singular form, with both people and things:

The pronoun todo (all, every, whole, entire) is inflected according to gender and number. A definite article is often used after it:

These non-independent indefinite pronouns are inflected according to gender and number, too:

The pronoun bastante (enough) is only inflected in singular and plural:

bastante comida = enough food

bastantes amigos = enough friends

The pronoun varios (several) is only used in plural form and inflected according to gender:

varios libros = several books

varias manzanas = several apples

The pronoun cualquiera (any) becomes cualquier when it is used before a noun:

Cualquiera me vale.

Any one is fine for me.

Cualquier coche me vale.

Any car is fine for me.

The pronoun cada (every, each) is uninflected; it can be used with both masculine and feminine words, but only in singular form:

cada día = every day

cada semana = each week