Do you know what a pronoun is? It's a fancy word that means a word that takes the place of a noun. You know how you can say "he," instead of saying "John"? That's a pronoun!
Now, a relative pronoun is a special type of pronoun that connects two different parts of a sentence that are talking about the same person or thing. For example, let's say I want to tell you about my teacher. I could say "My teacher is Mrs. Smith. She is very nice." See how I used the pronoun "she" to talk about my teacher after I already said her name? That's a relative pronoun!
Some common relative pronouns are "who," "whom," "whose," "that," and "which." They all help connect two parts of a sentence that are talking about the same person or thing. So, next time you hear someone using a pronoun to talk about something they already mentioned, you'll know they're using a relative pronoun!