Brake fluid is a specialized liquid used in hydraulic brake systems to transfer force from the brake pedal to the brake components. It is essential for the proper functioning of vehicles, as it allows the brakes to engage and stop the vehicle effectively. There are different types of brake fluid, including DOT 3, DOT 4, and DOT 5, each with varying properties and boiling points. Regular maintenance and checking of brake fluid levels are crucial for safety, as low fluid levels or contaminated fluid can lead to brake failure.