Files and directories in the UNIX File System have a set of "permissions" that determines who is allowed access to them. The permissions are "read" (the ability to read or copy the file or directory), "write" (the ability to edit, delete, or otherwise change the file or directory), and "execute" (the ability to execute a program file or to change into and browse a directory). The level of each of those permissions is assigned to each of 3 different types of people: the owner of the file (e.g. you own the files in your home directory), members of the owner's group (a group can be comprised of any set of users), and the world (everyone else with an account on the computer, not really the whole world).
I find it interesting to see how Linux has made itself visible in – well, many fields. This page shows some occurrences of Linux/Unix in some (more or less) main-stream daily cartoons.
links for 2008-10-055 10 2008