Actually, it is "ugo"

u = user (owner of the file)
g = group (group that the file belongs to)
o = others (users that aren't the owner and aren't a member of the group to whom the file belongs)
a = all

`chmod 700 file` gives only the file's owner the ability to read, write and execute the file.
`chmod go-rwx file` does the same thing (removes group and others permissions to read, write and execute).

`chmod a+rwx file` gives all users and groups the ability to read, write and execute the file.
`chmod 777 file` does the same thing.

You can also specify separate things like "a+x" (allow all users to execute a file) or "o-w" (allow only the owner and owning group to write to the file by disallowing others write access).

Some commonly used ones are:
755 - allow read/execute access to all, and allow the owner to fully manipulate the file
744 - allow read access to all, and allow the owner to fully manipulate the file
700 - only allow the owner to fully manipulate the file
644 - allow read access to all, and allow the owner to read from and write to the file
500 - only allow read/execute access to the file
000 - is this even used? perhaps by a newbie... who would want to disallow ALL access?

I have yet to figure out how umask values work though. The whole four-digit thing is what gets me. :P

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Waiting patiently for Windows 7, XHTML 2.0, CSS 3.0, PHP 6.0, the ratification of C++0x, and the day that I can code without logic troubles.