Collaboration: We need a virtual reality world for the participants to communicate with each other and to see what each other are doing in sync.
One way to do this is to have a large shared display showing a single virtual world where multiple people in the same location share that virtual world where one person controls the viewpoint but one or more people might have interaction control. The participants see each other's real bodies, and talk to each other directly. This is co-located collaboration.
If the participants are not co-located then more infrastructure is needed. In this case each participant is in their own virtual world (whether via HMD or a large display) and is connected via a server to other participants sharing the same space. Participants have avatar bodies - representations of their tracked selves in the virtual world for others to see - and voice (and video) is streamed between the participants.
More recent examples: