What kind of pronoun is the word '' what''?

The pronoun 'what' is an interrogative pronoun, a Word that introduces a question.

The pronoun 'what' takes the place of the noun or pronoun that is the answer to a question.

Example: What do you want for lunch? I would like some soup.

The pronoun 'what' can also function as a relative pronoun to introduce a relative clause.

Example: I understand what you said.