An Office 365 group is a Security Group within Azure Active Directory.
Groups have their own permission model that comprises the roles Owner and Member.
- Owners: manage the group (e.g. changing titles, managing members and privacy settings)
- Members: collaborate around content (e.g. conversations in Yammer and Outlook, documents within a SharePoint team site)
If the admin deletes the owner of the Security Group, this user no longer has Full permission of this site collection and cannot access the site collection. Unless the admin grants access permission to the user later.
Delete user from Office 365 Group(Security Group) owners.
This user no longer has Full permission of this site collection and cannot access the site collection.
Office 365 Groups are a new breed of security groups. It is not just a security group, but a security group with “benefits.”
You can read more about an Office 365 Group here.