titles - PhD candidate vs PhD student

I see researchers working on their PhD calling themselves PhD Candidates, other call themselves PhD students. What's the difference between a PhD Candidate and a PhD Student?

According to two posters on the WordReferences forums:

This terms vary from university to university, usually a PhD student is granted the candidate status after completion of a “comprehensive examination”, which occurs sometime after the first year.

and

Here in the U.S., a “Ph.D. Candidate” is a student who has completed all of the academic requirements for their degree, except their dissertation.

So this works in the USA and Canada I presume, because they have structured PhD programs where you attend courses as part of your PhD. Unlike most of the universities in Europe where a PhD student starts off directly with his/her PhD thesis. (Europe does have structured programs as well, but they are not as widely spread yet).