In linguistics and grammar, a pronoun (abbreviated ) is a word or a group of words that one may substitute for a noun or noun phrase.
Pronouns have traditionally been regarded as one of the parts of speech, but some modern theorists would not consider them to form a single class, in view of the variety of functions they perform cross-linguistically. An example of a pronoun is "you", which can be either singular or plural. Subtypes include personal and possessive pronouns, reflexive and reciprocal pronouns, demonstrative pronouns, relative and interrogative pronouns, and indefinite pronouns.
The use of pronouns often involves anaphora, where the meaning of the pronoun is dependent on an antecedent. For example, in the sentence That poor man looks as if he needs a new coat, the meaning of the pronoun he is dependent on its antecedent, that poor man.
The name of the adjective that belongs with a "pronoun" is called a "pronominal". A pronominal is also a word or phrase that acts as a pronoun. For example, in That's not the one I wanted, the phrase the one (containing the prop-word one) is a pronominal.
Pronoun is a category of words. A pro-form is a type of function word or expression that stands in for (expresses the same content as) another word, phrase, clause or sentence where the meaning is recoverable from the context. In English, pronouns mostly function as pro-forms, but there are pronouns that are not pro-forms and pro-forms that are not pronouns.[p. 239]
Examples [1 & 2] are pronouns and pro-forms. In [1], the pronoun it "stands in" for whatever was mentioned and is a good idea. In [2], the relative pronoun who stands in for "the people".
Examples [3 & 4] are pronouns but not pro-forms. In [3], the interrogative pronoun who does not stand in for anything. Similarly, in [4], it is a dummy pronoun, one that does not stand in for anything. No other word can function there with the same meaning; we do not say "the sky is raining" or "the weather is raining".
Finally, in [5 & 6], there are pro-forms that are not pronouns.