Maybe that needs qualification, because "betas" are generally/always(?) numbered lower than 1.0, but I've seen "release candidates" numbered higher than 1.0.

Can anybody clarify?

"Beta" and "preview" usually mean the same thing. The only difference in terms of common usage is that many (not all) beta versions of software are closed--for example, you will never (legally) see a beta version of Photoshop floating around for all and sundry to use, they're kept close by Adobe--whereas a preview release is equivalent to something like a "public beta" (an early version that anyone can see).

A release candidate (RC) version is a version that's very close to being finalized. It's still beta, but unlike a normal beta, it's feature-complete; the author is not planning to make major feature changes, or interface changes, or anything like that. At this stage, it's bug-fixes only. Sometimes, the released version of a piece of software is identical to the last release candidate version.

Thanks.