Servers and hosting
Root access
Full administrative control of a server: install anything, change anything, and be responsible for all of it.
Root is the superuser on a Unix system. With root access you can install and remove software, change any configuration, open and close ports, create users, and run services on any port. It is what separates a VPS from shared hosting, where the provider holds root and you get a panel.
With the control comes the maintenance: updates, firewall, backups and the mail server's reputation are yours. The first things to do on a new server are to log in with an SSH key rather than a password, keep a non-root user for daily work with sudo for the rest, enable automatic security updates, and open only the ports you serve on.
Providers can help around the edges, with a console when SSH is unreachable, a reinstall from the panel, and snapshots, but they do not manage the software inside. If you want someone else to hold root and keep it patched, that is managed hosting, a different product.