BRAKE shudder is probably what they mean. After a while the disc can become uneven (Either through warping, or just the way the disc has worn amongst other reasons) and this causes brake shudder which you can feel through the pedal. They then machine the disc surface which re-smooths it, eradicating the brake shudder.
What u are refering to is brake shudder or brake pulsation some also refer it to.
The only way to rectify the problem is for the disc rotors to be machined. so the disc runs true again.
Brake shudder is caused by warped or out of round disc rotors, or even hot spots.
What causes brake shudder, is when the disc rotors reaches a high temperature of expansion, this doesnt cause brake shudder at all, the cause of brake shudder is when the disc rotor is hot eg, after continous braking, and the pulling up to a complete stop, and staying stationary, which causes massive heat spots in the rotors where the brake pads are clamped by the caliper, at this point the rest of the exposed cliper is cooled by air, to the rest of the exposed area, hence called warping of the rotors.