This question makes me feel old. And I'm in my early twenties.
I started in computing with an Apple II+ (not really - my II+ was only the first to have floppies). I always wondered why those poor CP/M (and MSX) users had to put up with such nonsense as drive letters ;-)
fd0: was floppy 1. If you had an additional drive, that would be fd1: etc. The best part was that you could also access devices by file-system label, so if you needed to make sure you were accessing not only a floppy, but the device labelled "WorkbenchExtras" you would simply do WorkbenchExtras:
Needless to say, this made multi-disk tasks & scripting rather pleasant, easy and cut out lots of boilerplate and checking.
It was a nice system and I kinda miss it.
Edit: df0: was floppy 1. dh0: was first harddrive, etc. Not that in changes much.