 Relative pronouns, definition, rules, and useful examples. So what exactly are relative pronouns? Let's take a look at relative pronoun definition, useful grammar rules with example sentences and an ESL printable infographic below. What is a relative pronoun? A relative pronoun is used to join or relate two different clauses together, by referring to the noun in the previous clause using the following pronouns, who, whom, who's, which and that. Relative pronouns, rules, which and that are generally used for objects, while who and whom are used for people, and who's is used to show possession. Let's take a look at some examples. She will choose the color which looks good on everyone. In this example, which joins the two related clauses about choosing a color, and the color which would look good on everyone. There is a car in the parking lot that someone has painted a bright pink. In this case, that joins the two sentences related to the object, and its location in the first and its appearance in the second. He needs to know by tomorrow who will be accompanying him on the business trip. Who here stands for the unknown person, and it also joins the two different clauses together. Is there anyone here whose cell phone has a signal? Who's in the example above is used to ask, if anyone has possession of something that the speaker needs.