sudo, which is short for "super user do" is a command that allows a user to perform tasks that require superuser, or root, permissions, without logging in as root or assuming root abilities full-time. It's usage is common in distros aimed at new users, who might not be aware of the consequences of logging in as root.
sudo is used to perform tasks that a normal user is not allowed to do. In this example, the user might want to upgrade the software on his system:
~# apt-get dist-upgrade
Since the user is not logged in as root, the system will return something like:
E: Could not open lock file /var/lib/dpkg/lock - open (13 Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?
If the user were to execute the same command using sudo, however:
~# sudo apt-get dist-upgrade
he/she will be prompted for their password, and then the command will execute normally.
- http://www.gratisoft.us/sudo/man/sudo.html The man page for sudo.