root is the login name of the top level administrator in a Unix-like operating system, such as Linux. This user is special in many ways. For example, no file protection flag can prevent the root user from viewing, executing, changing or removing files and directories.
As a result, many system level functions must be performed by the root user (instead of a regular user). Such functions include system update, software installation, service starting and stopping, configuration file editing and etc. Essentially, root can do anything if it can be done, at all.