The clutch disc is a part of the clutch assembly. It is a friction disc that connects the engine and the input shaft of the transmission. The clutch disc allows the engine and transmission to temporarily disconnect so the driver can shift gears.
The most common failure of the clutch disc is deterioration of the clutch disc material. Once the disc wears out, then it will have to be replaced.
Most manufacturer factory warranties and extended warranties do not cover the clutch disc. However, it still needs to be maintained in order to ensure the validity of your manufacturer factory warranty and extended auto warranty, if applicable.