I originally posted this back in 2009 on the SMG forums.
We had a little confusion in our raid Saturday so I wanted to better explain what we were try to convey. During a boss fight we were telling everyone to stack up. The dictionary defines the word stack 11 different ways. For raiding purposes we are concerned with #2.
stack (stāk) n.
1. A large, usually conical pile of straw or fodder arranged for outdoor storage.
2. An orderly pile, especially one arranged in layers. See Synonyms at heap.
3. Computer Science A section of memory and its associated registers used for temporary storage of information in which the item most recently stored is the first to be retrieved.
4. A group of three rifles supporting each other, butt downward and forming a cone.
-a. A chimney or flue.
-b. A group of chimneys arranged together.
6. A vertical exhaust pipe, as on a ship or locomotive.
7. An extensive arrangement of bookshelves. Often used in the plural.
8. stacks The area of a library in which most of the books are shelved.
9. A stackup.
10. An English measure of coal or cut wood, equal to 108 cubic feet (3.06 cubic meters).
11. Informal A large quantity: a stack of work to do.
v. stacked, stack ing, stacks
In the real world two objects cannot occupy the same space at the same time but in the game world they can. When we tell you to stack up we literally mean that everyone should be standing in exactly the same spot. There should only be one set of foot prints with each next person standing on the previous person’s feet.
Are there exception? Yes. A hunter may need to take a half step back so he can still shoot or a melee attacker may need to step up. If you need to do that you can in most situations, but you must first stack up with the rest of the group then make your adjustment. You should never assume that you are going to need to be in a different spot until you have stood in the place you have been directed too.
The stack order will always be followed by a location. “Stack up on the tank.” “Stack up on the Star.” etc. Stacking is used for a number of reasons but almost always to save your life. in Cel’s example [below] if you are not stacked up with the people who have the same debuff as you, you will kill the rest of the raid. if you remember back to the Attumen fight in Kara we would stack up on the horses butt to keep him from charging a party member.
Molten Core (MC) was a great example of a raid where you had to know how to stack properly. in that example you had to stack on the mob itself as opposed to a designated player. because of the way this looks on screen and in true SMG fashion we call mob stacking either “hugging” or “licking”.