Desktop versions of the classical guitar, violin, and cello photos from Mierswa Kluska's Inside the Music series from a little while back, should anyone want:
The "-rf" bit is the options, in this case do everything recursively (r), i.e., go through all the folders from top down, and (I think) "f" forces the erase, regardless of file permissions, etc.
"/" is the symbol for your harddrive.
So, if you put "rm -rf /" into a Unix computer (say, a Mac or a Linux machine) and you have sufficient privileges, you'll delete the entire HDD.
For those with an open mind, wonders always await! - Kilton (monster enthusiast)