From Diablo Wiki
Hell incan mean one of the following:
Game Difficulty: Hell
When starting your first character in Diablo II, you will automatically have a character starting on 'Normal' difficulty setting. This difficulty setting dictates monster hit points, damage, immunities etc. It's mathematically impossible for a starting character to survive in any other difficulty setting than Normal (if it was possible to do that). When a character kills Diablo, he can then continue to the Nightmare difficulty, playing the game again. When Diablo is vanquished on Nightmare setting, a last testament on Hell difficulty can start.
This is just part of the material available on this topic. The'Hell' article is also available in the main wiki where a lot of new information has also been made available after the announcement of Diablo III. You can find it here:
- DiabloWiki.net/ .