Instance is a term used to describe areas of a MMORPG that are generated when a player or small group of players enters into them. Many copies of an instance can be running at the same time. In DC Universe Online there are the following types of instance.
Iconic Battles. Solo content where a player enters the lair of a established DC hero or villain. Players will be led into these instances by quests but can repeat them for the purpose for getting Solo Content Feats
Alert Zones Balanced around a small group of four people spread throughout the leveling experience starting at level 9. There are also Hard Alerts which are end game 4 player instances used by level 30 players to gear up for raids which are more difficult and cannot be successfully attempted by a group of people who have just finished leveling to 30.
Duos End game 2 person content.
Raids End game large group content.