The Boulder Badge is a Pokémon League badge awarded to trainers who defeat the Rock-type Gym Leader, Brock, in the Pewter City Gym. It signifies that the trainer has successfully challenged and overcome the Gym's challenges, demonstrating their skill in battle. This badge allows trainers to command Pokémon up to level 20 and enhances the effectiveness of Rock-type moves. Additionally, it grants access to the use of the move Flash outside of battle, which is useful for navigating dark caves and areas in the Pokémon world.