A "papercraft" or physical 3D ring model made of high-quality "deep" paper stock.
Modern papers suggest that using a "multi-scale structural similarity index" (MS-SSIM) helps the AI understand the geometry better, leading to "perfect" visual corrections in 3D models.
I am answering for the first interpretation, as "deep paper" most commonly refers to in technical contexts. Technical Context: 3D Ring Artifacts & Deep Learning
Inpainting of Ring Artifacts on Microtomographic Images by 3D CNN
Researchers often use 3D Convolutional Neural Networks (CNNs), like the U-Net architecture, to "paint over" or remove these ring-shaped defects in 3D scans.
A specific "Deep" rendering style or texture applied to a 3D character like Tamaki.