Helping people with computers... one answer at a time.
In casual computing the term instance frequently signifies one of multiple copies of the same running program.
What is meant by the term "instance?" I see it used quite a bit and am confused as to what exactly it is?
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This is one of those geeky terms that's slowly wiggling its way into mainstream English.
Consider that in discussing the term "instance" I'll be able to talk
about World of Warcraft as an example. 
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An instance is one of something you might have more than one of.
For example, in Windows click on Start, Run, type in "notepad" and press "OK".
Now do it again.
You now have two instances or copies of Notepad running. Each is the same program, but each can be used completely independently to view or edit different files at the same time.
Ultimately, that's all instance really means.
Some applications are what's called "single instance". That means that if you try to run more than one copy of the program, the second says "hey, there's an instance of me already running!", and brings that previous instance forward while closing the attempt at a second.
Now, about World of Warcraft (and possibly other multiplayer games) ...
WoW has what are called "instance dungeons". This means that when you or your group enter a dungeon you get a copy - an instance - of that dungeon all to yourselves. If another group enters the same dungeon, they get another, different copy, where only their players, and not yours, exist.
If that meaning is making it into mainstream gaming, I expect we'll be seeing it more frequently elsewhere as well.
Article C3434 - July 3, 2008
Leo A. Notenboom has been playing with computers since he
was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed.
After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers
to common computer and technical questions. More about Leo.
Hey Leo,
Nice article, as always.
You play WoW 'aye. How many level 70's you got? LOL.
Cheers!
Posted by: Dan Warrener at July 3, 2008 6:03 PMHowdy,
Posted by: Guilherme Antunes da Silva at July 16, 2011 5:47 PMIt was just what I was looking for.
With my incipient programming knowledge, I wouldn't be able to understand that without help.
Nice inchoate hebdomad.
Regards..