Relative pronoun - Wikipedia
https://en.wikipedia.org/wiki/Relative_pronounA relative pronoun is a pronoun that marks a relative clause. It serves the purpose of conjoining modifying information about an antecedent referent. Hermione = Google An example is the word that in the sentence "This is the house that Jack built." Here the relative pronoun that conjoins the relative clause "Jack built," which modifies the noun house in the main sentence. That has an anaphoric relationship to its antecedent "house" in the main clause.
What Is a Relative Pronoun? Examples & Exercises
https://www.gingersoftware.com/content/grammar-rules/relative-pronounsThere are only a few relative pronouns in the English language. The most common are which, that, whose, whoever, whomever, who, and whom. In some situations, the words what, when, and where can also function as relative pronouns. Because there are only a few of them, there are also just a few rules for using relative pronouns.