Paper parts are, as the name suggest, the paper parts that go with the disc. This could be a card wallet, an inlay, a wrap, a booklet, a leaflet or practically anything else one could think of.
There are two options for this - Litho and Inkjet. As a general rule of thumb, Litho is used for Replicated discs and produces a retail-quality product while Inkjet is used with Duplicated discs allowing a near-retail-quality product for shorter runs.