People will often describe the vast groups of files and directories (a directory is just a slightly more techy name for folder) as a tree. However, that is nowhere near cool enough for me. I suggest, before we get into the nitty-gritty of talking about file systems, you watch this video. When the guy washes the dirt off of the ant-hill cast, you will see how the whole thing extends from a central stem and then grows lots of smaller, more localized tendrils.