What does a star represent in project group assignment?

If a project is assigned to multiple project groups, BQE CORE allows you to define one group as the default for that project and that default group is prefixed by a 'star' icon. This applies not only to the Projects screen, but to all the CORE screens that allow assigning of groups such as Clients, Employees, Vendors, Leads, Prospects, etc. Check CORE Help Center > Projects for details.