Alpha (Rift)  

Alpha testing is from ~unknown~ to ~unknown~ and participants were invited and placed under NDA

Wikipedia

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 usually occurs eight to ten months before code release.

References

• Wikipedia: Game Development

RIFT Wikibase™ Patch Notes