The sudo command is a program for some Unix and Unix-like operating systems that allow a user to execute programs with the security privileges of another user. Typically those of a superuser or the root user.
Through a configuration file, usually known as a sudoers file, an administrator of the system can delegate authority to certain users and give them the ability to run the specified commands as a root or as another user. The sudoers configuration file can also be configured to provide a log those commands usage and what their arguments were.
Users typically execute a command to which they want to have elevated privileges by prefixing their command with the sudo command:
allan@company$ sudo vim /etc/group
If the user allan has been configured on the sudoers file to gain access to the /etc/group file, a password prompt will be shown and once allan introduces his password, vim will launch and allan can edit the /etc/group file with the same privileges of the root user.
If allan isn't a part of the sudoers configuration file, he will instead receive an error indicating he does not have access to /etc/group and cannot perform the command vim /etc/group.
On both cases the system will log the occurrences. A system administrator can later review these logs and audit all uses of the sudo command.