Rogues are cats that don't belong in any clan. They have no specific territories and hunt anywhere they want, and for themselves. They follow no rules and are quite free.
The most commonly known rogue clan is DeathClan, hence the cats' one-worded names and nature. They're similar to normal clans, as they have rules and territory, but take on much of a rogue's attributes. There are also rogue clans some cats' decendants come from or current cats have once owned, such as TigerClan and SharpClan. Mainly DeathClan cats are related to these older rogue clans, such as Fawn and Scorch.