Instance

An Instance is a copy of a zone. While in the instance, you will only see other players that are within the same copy of the instance. There are many kinds of Instances:
Public Zone: Not restricted to one person, group, or raid, all may be present in the zone at the same time. When more than 100 players are present in any public zone, an instance of the zone will fork. If you are zoning into a zone that has forked, you will get a box asking you which instance of the zone you wish to enter. Make sure everyone in your group goes to the same instance!
City/Village Zone: Same as a Public zone except that they will not fork a new instance no matter how many players are present in the zone.
Housing Instance: An Inn Room or House is also an instance. It is Public, but there are restrictions possible on who may enter which are set by the owner.
Tradeskill Instance: A zone where only crafting occurs. The tradeskill instances in Qeynos share the same general layout while those in Freeport share a different layout. No other zones have instance specifically designed just for tradeskills.
Dungeon Zone Instance: Most dungeon zones are Instanced. This means that when you and your group or raid enters, you all zone in together and face a pristine copy of the zone. No mobs will be missing, all named are present and noone else can camp your mobs. In some instances the mobs you have killed will respawn so you can adventure endlessly within the instance. Most instanced zones, however, do not re-populate (re-pop). There are 6 possible dungeon zone instance styles:
*Solo: The zone may or may not allow more than 1 player to enter, but it is designed for 1 player to complete.
*Solo-Group: These zones give a choice to enter a Solo version or a Group (Heroic) version.
*Group: The zone is designed to 3-6 players. It might not allow you to enter with fewer than 3 players.
*Group-Raid: These zones give a choice to enter a Group (Heroic) version or a Raid (Epic) version.
*Raid: Depending on the specific quest, 6-12, 12-18 or 18-24 raid members will usually be REQUIRED to enter the zone. At the very least you should be sure to HAVE that many before attempting this zone.
*Public Raid: very rare, there are only a few of these in the whole game. Often called Contested, these are Raid zones that behave like a Public zone. Mobs re-pop, your raid is not the only group possible, and disputes over camps can arise.