My gut says code name or nickname, but if there's any truth to Ark Theory...
In the original Odyssey by Homer, Odysseus is trying to sail home to Ithaca after the Trojan war and is given a bag of winds containing all the winds but the west to speed his journey. However just when they are in sight of Ithaca his crew open the bag (thinking he is hiding gold) and the winds blow his ship a great distance away leaving them to embark on the Odyssey to get home again.
We know that the galaxy map does not look like the milky way. They said we would be surprised at the distance. There are rumors the game will focus on exploration. The Ark theory is interesting but as presented it really does have problems. Under any sort of conventional travel it would take hundreds of years to simply leave the galaxy. In which case the ark would be hit by the events of the crucible before it even got out of first gear, hence not really avoiding ending issues. Furthermore why wouldn't they simply turn around once the Reapers were defeated?
There may be more to it. The people behind the ark may have a secret relay, wormhole or something else. However yesterday, as something of a joke, I presented another idea where a chunk of the fleet that were near the relay when the crucible blew would be relocated by some reaction around the different bursts of energy and could in fact move them to another galaxy (similar but not the same as Star Trek Voyager). It was inspired by seeing the Normandy "appear" on that alien planet after trying to flee the crucible blast. However seeing that shirt and seeing their team named "Odyssey" bares an eerie resemblance to the premise of the ancient poem.