Here's why:
* Pronoun: It replaces a noun or noun phrase (e.g., "Some of the students are late").
* Indefinite: It doesn't refer to a specific person or thing, unlike a definite pronoun like "he" or "that".
Indefinite pronouns often refer to an unspecified quantity or number. Other examples of indefinite pronouns include:
* all
* any
* each
* everyone
* nobody
* several