This is an excerpt from a July 2006 article in CardMaker magazine:
Card Crafting Basics
Card crafting is easy, creative and fun. Collect basic tools and supplies, learn a few simple terms and techniques, and you're ready to start. The possibilities abound!
Scoring and Folding
Folding - Mountain folds-up, valley folds-down. Most patterns will hae different types of dotted lines to denote mountain or valley folds.
Tools - Scoring tool and bone folder. Fingernails will scar the surface of the paper.