Differences between mods versions

[Hellvard]

I always wondered about why certain mod is for example in Alpha version. What is needed to achive this status? What is essential to include in mod to release it in such version and what can be ommited? How many bugs are allowed for alphas? And what about betas? How much progress has to be made from alpha to release mod in beta version? Is there any non-written codex of releasing mods or is it all up to the modder himself?

[Gigantus]

alpha - barely working mod, likely to crash, 'proof of concept'.
beta - reasonably working but crashes have to be expected, 'user input for bug hunting'.