Background
Prior to the introduction of Skill sets, the only way to assign skills to a person was via teams. As such, when a new instance was created, a default team was automatically created in the background named "(no team)" which has all of the skills in the system assigned to it. All people added to the system would automatically be assigned to this team. This is the way that skills were assigned in instances where customers had not created their own teams.
The "(no team)" team remained hidden until a customer added their first team to the system. It would then be displayed in the Teams Directory, but was not able to be deleted (however could be renamed).
Changes to the (no team) team
Since the introduction of skill sets, skills can now be assigned to people by team, role, or custom. Therefore, it's no longer necessary to enforce that each person is a member of a team. As such, we now allow customers the ability to truly have people that are not members of any team (including hidden ones).
To avoid confusion between people that are truly not assigned to any team, versus people that are assigned to the "(no team)" team, it has become necessary to rename the "(no team)" team to "(Unnamed team)" for clarity. If customers have already previously renamed "(no team)" to something else, they will not be affected.
What you should do next
There is no action required on your part. Everything will continue to work as it has in the past, with the exception of "(no team)" being renamed to "(Unnamed team)".
If you desire, you can rename or delete this team. If you delete it and there are people assigned to the team at the time, they will no longer be part of any team. If those people have their skill set configured to "Use team skills", they will not be able to start any new assessments until they are assigned a skill set that contains skills. For more information about skill sets, see the Skill sets support page.