Hi,
What is the purpose of Department and Team in people? What is the difference between these two and Group?
Please help.Thanks in advance
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If you're not inclined to review the documentation, then the summary answer, as indicated by jayap , is that Teams and Departments are deprecated.
Right now you can expect backwards compatibility for existing teams and groups, but you should avoid creating solutions that depend on teams and departments going forward. Use Custom Groups instead.
If you're just starting out, consider reading the playbook play for Application Authorization to assist with your application design plan.