I've come across many apps on the web that call themselves Beta. I've come across other apps that had an alpha designation. I've even come across some that called themselves pre-alpha, whatever that means (if you know please clarify). Then I've come across some really bad webapps that shouldn't have left the developer's computer and they didn't have any beta designations. I've also seen some well built apps that called themselves Beta, including Stack Exchange (the mother site of SO) which I believe is very full featured to be called a Beta.

I'm a little confused. It seems people are doing it at their whims. Is there an established rule or a checklist that can help decide what stage an app is in (beta, alpha, pre-alpha, or none)?

P.S. Please feel free to retag as appropriate.