“Brake rotors, also called discs, are an important component of the braking system on any vehicle. The brake rotors are the part of the braking system that gets clamped down on by the brake pads, stopping the wheel from spinning.
There are several different types of discs:
Drilled: These have holes drilled into them to allow for the release of heat and gas build-up. These are also helpful for driving through wet weather, the drilled holes allowing water to move through the rotors, but not pool.
Slotted: Brake rotors are slotted for the same reasons that rotors are drilled but are also stronger and less likely to crack. These make them the most popular option for vehicle owners.
Smooth: Smooth brake rotors are best when used on cars that aren’t subjected to aggressive driving conditions such as rush hour traffic. They are often used on luxury cars.
Slotted and Drilled: Slotted and drilled brake rotors give the stability of slotted rotors with the heat tolerance of drilled. Previously only available as an aftermarket upgrade, they are being included in stock packages on some models today.
Two-Piece Floating: These brake rotors are best used on vehicles that are driven in high-heat situations, such as in cities with many hills. Two-piece floating brake rotors do not do well in areas where salt is a standard winter road treatment.
The brake discs on a vehicle can last anywhere from 50,000 to 120,000 km – and sometimes more. A licensed and trained mechanic can evaluate the discs and advise you on their status; they may not need to be changed as often as the brake pads. Like brake pads, they should be replaced in pairs.
Discs can sometimes be resurfaced (also known as skimmed), depending on the amount of wear. When discs are skimmed, a mechanic grinds down their surface and makes them smooth and flat again. This will only work if they are not warped or cracked.
h/t to yourmechanic.com for this info!