That sensation is best described as a pulsation or vibration through the brake pedal, steering column, and the vehicle's body while braking. The frequency of the pulsation is proportional to the vehicle speed.
It is due to warped rotors or drums.
Just had the front rotors turned on my wife's car about two weeks ago. Same problem. Seems mine warp after avery trip to Firestone for rotate and balance..... and these are cryo-treated rotors. $120 each and have been turned twice. Next time, I'll just buy the $40 ones and keep the car away from the impact wrenches the Firestone monkeys use.
Stev e