Yes, the nomenclature has changed. On DU3 we designated forums as either "Forums" or "Groups" -- "Groups" was the designation we used for forums which were essentially user-created and hosted. There are technical differences between the way forums were managed vs. the way groups were managed, however, major obvious differences between them became narrower and narrower over time until, when we were working on the redesign, it became apparent that we might as well simply call everything "Forums" since that's the most obvious descriptor.
On the surface level, we now separate forums like this:
Main Forums: General Discussion, Latest Breaking News, and The DU Lounge. These are managed by the Main Forum Hosts.
Topic Forums: Every other forum. These are hosted by individuals with an interest in the particular topic (or not hosted at all).
However, in the underlying code, there is still a technical difference between forums and groups, which is why you might sometimes see the "Groups" designation cropping up occasionally. Over time we will go through these as we find them to bring them into line with DU4 standards, but these are really just text/labeling issues -- it's not going to make any difference to the way the forums operate.
There are also a few forums which retain the "Group" title even though they are now officially forums -- for example, the Asian Group, or the Jewish Group. We did not think it was necessary to change these titles.