Sometimes a brake pulsation is not from a bent rotor at all, but from hard spots - localized areas where the rotor metal has changed hardness. They feel like a warp but have a different cause. Here is what rotor hard spots are.
What hard spots are
Hard spots (or hot spots) are patches where the cast iron has been heated so severely that its structure changed and hardened. These raised, harder zones sit slightly proud of the surrounding metal, so the pad rides over them unevenly - producing a pulsation through the pedal.
Why they feel like a warp
Because hard spots create thickness variation, they cause the same pulsing you get from a warped or uneven rotor; see warped rotor causes. Much of what drivers call warping is actually uneven pad deposits or hard spots rather than a truly bent disc; see pad transfer layer.
What causes them
Severe overheating - riding the brakes, a stuck caliper, or an aggressive stop from high speed - can create hard spots; see why brakes get hot. Once the metal has transformed, the spot stays harder than the rest of the rotor.
How to fix
Hard spots usually cannot be machined away permanently - the hardened metal resists cutting and often returns, so replacement is the reliable fix; see resurface vs replace. Fit quality rotors, fresh pads, and new hardware, and avoid overheating.