It's the part that the wheel bolts onto and allows the brakes to stop the vehicle.
There is a picture one here.
http://thumbs300.1aauto.com/BRR/1ABRR00023.jpg
Two wheel or Four wheel drive?
It is what the brake rotor fits onto.
The wheel hub holds a wheel, or in some front drive vehicles a brake rotor holds the wheel and fits on a hub
You usually have to take off the brake caliper, then the caliper mounting bracket to free the rotor.
Remove the wheel, remove the caliper, and the rotor will just come off.
if it is all wheel ABS it right behind the rotor and goes into the front wheel bearing and if it is not all wheel ABS it is the back wheel behind the rotor
The front brake rotor, on a 2004 Chevrolet Colorado, can be removed by first removing the wheel. Next, remove the brakes. The rotor will slide off
No, you can remove and/or replace the front rotors on your Jeep Liberty without having to repack the wheel bearings. To remove the rotor, remove the brake caliper, and then pull the rotor straight off the wheel studs. If the rotor doesn't budge, then use an air hammer to tap the front face of the rotor adjacent to the wheel studs (the flat area of the rotor directly between the wheel studs). This will knock the rust loose and let the rotor slip off the studs. DO NOT use the air hammer on the braking [shiny] surface of the rotor!
On my '90, the rotors are held in place by the wheel studs. I had to press the wheel studs out, then the rotor separated from the hub.
Worn bearings, loose rotor, warped brake rotor, sticking brakes.
Check the rotor, it's probably warped.
When you change rotor or main ball joint, or when they get worn.