Glossary
Pitch
The steepness of a roof, written as inches of vertical rise per 12 inches of horizontal run. A 6:12 roof rises 6 inches over every 12 inches.
In practice
Pitch decides which coverings are permitted, how much material the roof needs, whether an ice barrier extends further up, and whether anyone can safely walk it. Below about 2:12, asphalt shingles are not watertight.