"Who" is a pronoun used to refer to people or individuals. It helps identify or inquire about someone, often in questions or relative clauses. For example, in the question "Who is coming to the party?" the word "who" seeks to identify a person. In grammar, "who" can also function as a relative pronoun, linking clauses together. For instance, in the sentence "The teacher who loves science is here," "who" connects the subject teacher to the additional information about them. This usage helps provide clarity and detail in communication.