Backing things up means backing files, data up by some means like copying files from the hard drive onto removable media like floppy disks. That was the main means besides tape drives at one point until seeing cd and dvd burners available. Patching through a usb or parallel port even 1394 firewire is a more common way to see files copied or moved between two different systems as well as over a network in some cases.
The most common item seen at this time is either the use of an external drive casing where you simply slide in an internal type hard drive or simply buy and use an external type that connects through a usb port. Many with portable units(laptops, notebooks) will often find this as a good choice to safe keep and even transfer files from portable to a desktop.
