r The third-person singular personal pronoun used to refer to an inanimate object, to an inanimate thing with no or unknown sex or gender.
r The third-person singular personal pronoun used to refer to an animate entity of unknown gender.
r Used to refer to oneself when identifying oneself, often on the phone, but not limited to this situation.
r The impersonal pronoun, used without referent as the subject of an impersonal verb or statement. (known as the dummy pronoun or weather it)
r The impersonal pronoun, used as a placeholder for a delayed subject, or less commonly, object. (known as the dummy pronoun or, more formally in linguistics, a syntactic expletive)