Niente is very simple, niente means just nothing. From a practical point of view there is no problem at all. From a theoretical point of view there is a little problem. Normally niente / nothing is subsumed under the pronouns. The central function of a pronoun is to represent something. But nothing doesn't represents anything, nothing is just nothing. If someone has nothing, he has just nothing and not something because nothing is nothing. Therefore, we can't really say that nothing is an indefinite pronoun because it is neither indefinite nor a pronoun. It is not indefinite because it is very definite, it's just nothing and it is not a pronoun neither because it doesn't represent anything. But there is no grammatical categorie which really suits for nothing, so it is allright to subsume it under the indefinite pronouns.