v2.x.x Release Candidates - What is the difference between normal, test and dev?

[bluejedi]

When downloading the v2.x.x Release Candidate zip files different versions (named 'normal', 'test' and 'dev') of the firmware are included.

While I can image (some) meaning of 'test' and 'dev', what exactly is the difference between these normal, test and dev versions of the firmware?