Root access

In computing, the superuser is a special user account used for system administration. Depending on the operating system (OS), the actual name of this account might be root, administrator, admin or supervisor. In some cases, the actual name of the account is not the determining factor; on Unix-like systems, for example, the user with a user identifier (UID) of zero is the superuser, regardless of the name of that account; and in systems which implement a role based security model, any user with the role of superuser (or its synonyms) can carry out all actions of the superuser account. The principle of least privilege recommends that most users and applications run under an ordinary account to perform their work, as a superuser account is capable of making unrestricted, potentially adverse, system-wide changes.

In Unix-like computer OSes, root is the conventional name of the user who has all rights or permissions (to all files and programs) in all modes (single- or multi-user). Alternative names include baron in BeOS and avatar on some Unix variants.BSD often provides a toor ("root" written backward) account in addition to a root account. Regardless of the name, the superuser always has a user ID of 0. The root user can do many things an ordinary user cannot, such as changing the ownership of files and binding to network ports numbered below 1024.

The name root may have originated because root is the only user account with permission to modify the root directory of a Unix system. This directory was originally considered to be root's home directory, but the UNIX Filesystem Hierarchy Standard now recommends that root's home be at /root. The first process bootstrapped in a Unix-like system, usually called init, runs with root privileges. It spawns all other processes directly or indirectly, which inherit their parents' privileges. Only a process running as root is allowed to change its user ID to that of another user; once it's done so, there is no way back. Doing so is sometimes called dropping root privileges and is often done as a security measure to limit the damage from possible contamination of the process. Another case is login and other programs that ask users for credentials and in case of successful authentication allow them to run programs with privileges of their accounts.

...
Wikipedia