What does Bart sell his soul for in The Simpsons episode 'Bart Sells His Soul'?

In the episode "Bart Sells His Soul" of The Simpsons, Bart sells his soul to his friend Milhouse for the price of $5. Bart initially believes the concept of the soul is meaningless, so he doesn't hesitate to make the deal. However, as the story progresses, Bart starts to experience a loss of identity and feels empty without his soul. This leads him on a journey to regain his soul and understand its significance in his life. The reason the answer is $5 is simply because that's the agreed-upon amount between Bart and Milhouse for the exchange of Bart's soul.