Difficulty

 is a rating given to a map depending on how hard the map is.

List
The main difficulty ratings are in this order, accompanied by their specific IDs:
 * 0 - Unrated
 * 1 - Easy
 * 2 - Normal
 * 3 - Hard
 * 4 - Insane
 * 5 - Extreme
 * 6 - Divine
 * 7 - Eternal

An additional "difficulty", Unknown difficulty, is used as a fallback in case the difficulty ID (which should be somewhere from 0-7) is invalid.