A relative pronoun is a pronoun that introduces a relative clause. It is called a "relative" pronoun because it "relates" to the word that it modifies. Here is an example:
The person who phoned me last night is my teacher.
In the above example, "who":
- Relates to "person", which it modifies
- Introduces the relative clause "who phoned me last night"
There are five relative pronouns: who, whom, whose, which, that.
Who (subject) and whom (object) are generally only for people. Whose is for possession. Which is for things. In non-defining relative clauses, that is used for things. In defining relative clauses (clauses that are essential to the sentence and do not simply add extra information) that can be used for things and people.
Relative pronouns can refer to singular or plural, and there is no difference between male and female.