A superuser account is a highly privileged account that can change system settings, create or remove users, and access restricted functions. On Unix-like systems this role is often called root; on other platforms it may be an administrator or local admin account. Because it sits above normal permissions, it can alter security controls, services, files, and logs.
In cyber attacks, superuser accounts are valuable because they give an intruder durable control. After gaining code execution on a server or appliance, an attacker may create a new superuser account to keep access even after the original flaw is patched. Defenders watch for unexpected privilege changes, new administrative users, and unusual authentication records, since those are common signs of persistence or abuse of legitimate admin rights. Strong password policy, least privilege, multifactor authentication, and account monitoring help reduce the risk.