Alpha is the stage when key gameplay functionality is implemented, and assets are partially finished. A game in alpha is feature complete, that is, game is playable and contains all the major features. These features may be further revised based on testing and feedback. Additional small, new features may be added, similarly planned, but unimplemented features may be dropped. Programmers focus mainly on finishing the codebase, rather than implementing additions. Alpha occurs eight to ten months before code release.
The definition of Alpha depends on whom you ask. If you ask producers, itís feature complete. If you ask programmers, they would like it to be feature complete, but know that itís not realistic. If you ask designers, itís the stage when designers get to test out all of their game ideas without even thinking about how many tasks being created by those ideas. If you ask artists, itís when designers and programmers stop adding new features, but in reality, they are certain that they reached Alpha when they get their first weekend off after many weeks of crunch time.
-From actual video game developers-