A group is a collection of maps and apps usually related to a specific area of interest. You can create groups as a way to organize your items. As a group owner, you decide who can find the group, if others can request to join, and who can contribute content. You also have control over items shared to the group and can invite others to join who have the same type of account you have—organizational or public, even if your group doesn't accept membership requests.
Groups that allow others to join the group and contribute items are a useful way to collaborate. For example, you might be a biologist working on an international bird habitat map template. You might search for groups whose members are sharing local bird habitat data that you could use. You could join the group and share your template. Together, your group could create a standardized international habitat map with rich local data layers.
Administrators configure the website by using groups to feature content on the home page and gallery and build custom galleries for basemaps and apps.
Administrators can also create groups that allow members of the group to update items shared with that group. These groups are useful for shift workers in operations centers who need to update maps underlying their apps and dashboards and other situations where multiple people need to update the same item. Members of these groups can also edit hosted feature layers that have been shared to the group with full editing control even if the layer is not editable. For example, a public hosted feature layer that isn't editable can be shared to the group and members of the group would have full editing control of the layer.