Each Marvel 'continuity' is assigned a designation that indicates its 'Universe Number'.
These are used to distinguish different (and often concurrent) timelines across comic books, television (including animation) and movie incarnations.
The Marvel Cinematic Universe has been assigned the designation: Earth-199999
Something about this designation seems to indicate that number has some kind of significance; both because of the seemingly deliberate recurrence of the number 9 and the designations length.
Most other continuities within the Multiverse have shorter designations, such as Earth-616 (Original Marvel Continuity) and Earth-1610 (Ultimate Spiderman). Others are made up of seemingly random numbers, Earth-818793 (Army of Darkness) or Earth-92131 (X-men Animated Series).
I imagine whilst some of those designations are likely to be totally arbitrary in their composition, I wonder if there is a reason why the Marvel Cinematic Universe chose such an interesting designation?