Scrapbook papers or otherwise known as design papers are not as thick as cardstock usually and have very decorative images. 

Sizes vary from 12 x 12, 8 x 8, 6 x 6 inches or other variants that are specific to scrapbooking. They can also be used for card making, art journaling, collages etc. Mad Arches mainly stocks Stamperia, Mintay, Ciao Bella, The paper Boutique and others.