You are using a WordPress Multisite installation where you can manage multiple websites from a single dashboard. It has an additional role that is above a regular admin, which is called Super admin. As the name indicates, the admin can manage a single website, but the super admin has the right to manage all of the websites under multisite installation.
Who should be Super Admin in WordPress Multisite?

Remember, super admin has all the rights to perform every task that is possible with WordPress, so it is the reason why it is most important to be careful when assigning this role to anyone. Ideally, keep your super admins as minimum as possible.

Most probably, business owners and higher management authorities have super admin access to all of the websites, but if you want to assign this responsibility and access to anyone so that he can manage your all websites.

Suppose you are a web development agency or freelancer web developer and manage multiple clients’ websites. In that case, it is better to make them an Administrator or Editor and keep sole super admin access at your own.

You have to create a new super admin user in WordPress multisite by visiting My Sites > Network Admin > Users and selecting the “Add User” button. After creating a new user (you can skip this step if you have created it already), change its role from the Edit User menu.

Full Article Source: https://www.temok.com/blog/super-admin-in-wordpress-multisite/