User blog comment:Jkphantom9/RWBY Recap Vol 2 by Asian Equation/@comment-4010415-20150821235629/@comment-24891101-20150822031342

Didn't Ruby say semester? I'd assume they use a semester system.

Volumes were the original plan, with two comprising a season, but that seems to have been abandoned, especially when their production corresponds to seasons (that is, yearly). Even RT's own organization of the episodes refers to them as seasons on their website.