A workspace is the top of the Work Center, and it is the boundary that decides who can see what.

There are two kinds. A personal workspace is yours alone — nobody in any organisation can see into it. An organisation workspace belongs to a company you are part of, and the people in it share the work. Within one, people hold a role: owner, admin or member.

Everything else is filed underneath it: workspace → project → folder → task. That is why moving something between workspaces changes who can see it.