Alpha essentially means that the game is "feature complete" and will now go through a rigorous polishing and testing period in order to make it the best it possibly can be.
The tid-bit was announced on the latest Crystal Dynamics podcast, with senior producer Kyle Peschel and art director Brian Horto stating that the game will be in alpha for at least two months. It will then go into beta for a further two months, putting the game's earliest release date at May. But in reality, don't expect it until Fall.
Elsewhere, in an FAQ posed on the Crystal Dynamics forum, global brand director Karl Stewart revealed that the developer is aiming for a "global, simultaneous release" for the game.
This is one of our most anticipated games of the year, so it's exciting to hear that the project is moving along nicely. We can't wait to play the final product. Fingers crossed it doesn't get delayed out of 2012.