Doctor Who, we are now getting an answer as to what it is and what it means.
This excerpt is apparently taken from the forthcoming The Tardis Handbook:
There is a crack in the wall on the Byzantium Flight Deck and it is in the same shape as the one in the previous episodes. The Doctor realises time energy is spilling out the crack, which erases every moment of existence of anyone it comes into contact with so that they have never lived at all. The angels call it the time field and predict that it will destroy reality. The doctor determines that the explosion that caused it is still happening, somewhere in time and traces it to a specific date, 26 June 2010, the wedding of Amy Pond.
The crack in the wall is present everywhere the Doctor and Amy go, and Rosanna Calvierri tells him she fled Saturnyne when her home planet was crushed by the silence as the crack snapped shut behind it. River Song already told the Doctor that he'll see her again when the Pandorica opens, something he thought was a fairy tale. But now he is aware something is very wrong in the universe - and its somehow connected to - and perhaps centered on - Amy Pond.
[Life, Doctor Who and Combom]