Slang, colloquial or normal?

[AndiFlatland]

There are many words in the dictionary which are described as 'slang' or 'colloquial'.
What I'd like to know is, how is it decided whether words are slang or colloquial, and at what point does a word stop being slang or colloquial, and become just another normal word and part of standard language?
I realise there is probably no particularly hard and fast line drawn in the sand on this matter, and each one will be different, according to usage and general acceptance. But these decisions are eventually made some time, and by somebody, so how and by whom?

[Quizmonster]

You've really answered your own question, Andi. It is simply a question of whether a word becomes sufficiently widely used and in what context. If a colloquial usage gradually creeps into formal writing and is accepted there, it will eventually be recorded in one dictionary or another as just an 'ordinary' word. If it is rarely used in writing at all, then it will remain colloquial.
In a sense, then, the only 'deciding' that happens is on the part of the editors of dictionaries.

[AndiFlatland]

Thanks for the response, Quizmonster!
I found it just as I had to finish my session in the i-caff (what chance of getting that one in the dictionary?!) the other day, so had no time to do more than rate it.
Yes, I suppose what you say makes pretty good sense, and I can't really add much more. It was just one of those questions that occurred in an idle moment, and I've forgotten the thing that triggered it now. I think it was some word I heard someone use in a radio programme, which I looked up in the dictionary and was surprised to find what I assumed to be a normal, everyday word described as slang.
Thanks again.