Team Project Groups
A team project group is a group associated with a specific team project. You can create any number of groups for your project, and grant them whatever project-specific permissions you want the group's members to possess.
Some team project groups are defined when your project is first created. The default groups that are included with Team Foundation Server are added to your project at its inception. In addition, all default server-level groups are added to the project; any custom server-level groups you might have created must be added manually. Any membership changes you make to server-level groups as part of the team project will be effective for all projects to which that group is assigned. Any permissions changes, however, are specific to the current team project.