Brake frequency is a setting on most ESCs. ESCs send power to the motor in bursts (cycles), and the frequency determines how many of these cycles occur per second.
A high brake frequency will make the braking response feel smoother, but it will deliver slightly less power. This works well with high-torque motors that need a smoother feel.
A low brake frequency may not feel quite as smooth, but it will feel more powerful. This will work well for lower-torque motors that just need a little extra punch when braking.
See our article on electronic speed controllers for more ESC settings.