Paper or cover stock, usually made by laminating two sheets of paper, is known as duplex paper. Each side is different. Duplex paper may be a different color on each side, have a different finish on each side, or different textures.
This is not the same as two-sidedness which is a natural occurrence due to the papermaking processing. Duplex paper is intentionally manufactured for special effects. Some uses of duplex paper include book covers, greeting cards, and presentation folders.