The milky way is one of many galaxies in the L-388 universe. In an infinate universe, there are an infinate number of parallel universes.
Universe L-388
This is the name given to the universe that we currently live in, as designated by the Time Agency.
There are an infinate amount of parallel universes, so the Time Agency have devised a numbering system to catalogue them all.
It is unknown what the number is based on, as the same number has appeared in many different places.