A group is a collection of one or many individuals.
You can have subgroups within groups. When a task is assigned to a group, any individual from that group or its subgroups can perform the task. For example, a financial company has three groups: Financial Analysts, Business Analysts, and Cost Analysts. Each group has expert resources. If you add the Business Analysts group and Cost Analysts group to the Financial Analysts group, any task assigned to the Financial Analysts group is available to members of the Business Analysts and Cost Analysts groups.