Brake fluid is a hydraulic fluid transmitting force from the brake pedal to the wheel cylinders or calipers, enabling vehicle deceleration. It’s utilized within the vehicle’s brake lines, master cylinder, and at each wheel’s braking mechanism. Modern brake fluids are typically glycol-ether based and categorized by DOT specifications (DOT 3, DOT 4, DOT 5, DOT 5.1) indicating boiling point and compatibility. Key characteristics include high boiling point to prevent vapor lock, low compressibility for firm pedal feel, and corrosion inhibition to protect brake system components. Maintaining correct fluid level and regular replacement intervals are critical for optimal braking performance and safety.