The Development Status of software defines how mature the software is.
Alpha[]
Alpha indicates that the code is very likely to be highly unstable, and is not recommended for use in a production environment. Alpha software typically isn't anywhere near feature complete, and severe limitations may be encountered during use.
Beta[]
Beta indicates one of many things, depending on where in the software world you are. Smaller developers may tag a build as Beta if they feel it is reasonably stable, and mostly feature-complete. However, many developers may wait until their software product is feature-complete, and then use the Beta development phase to iron out existing bugs, test server stability, and run simulations in preparation for a full release.
Release Candidate[]
Seen in both open-source and closed-source software, a Release Candidate is a statement from the company that says "We believe that this product is ready for an official release, however, additional testing is required to confirm this".
Full Release[]
Speaks for itself.