I'm a bit of a geek, and have understood for a long time that file systems are a key part of an OS, and that the end-user just shouldn't mess with this kind of stuff. So, I never really did. The link below is an Ars Technica article that goes through the history of file systems and explains exactly what they are – in a very engaging way. Well worth a read if you're at all interested in geeky stuff. From BFS to ZFS: past, present, and future of file systems
Geeky Stuff: File Systems
heads up: this is a pretty old post, it may be outdated.