Recursive definition

Recursive definition is a way of explaining something by using the same thing you're trying to explain over and over again until you get to a simple version. It's like if I asked you to explain what a toy car was, and you said "a toy car is a car that is made out of plastic" and then I asked, "What is plastic?", and you said "plastic is a material that is made out of chemicals" and then I asked "What are chemicals?" and you said "chemicals are tiny things that are used to make everything around us". You explained something by referring back to the thing you were explaining. That's what recursive definition means!