Since most of us deal with computers, you've probably come across the concept of the "root" directory. A disk drive may have many folders and files, but the folders are all stacked inside each other, except for one, the "root" that contains all the others. The word "root" suggests a structure with its base in the ground, and all the complexity flowing upward. These directory stacks can also be referred to as "trees," in which branches represent folders containing more folders (smaller and smaller branches) until you get all the way up to the leaves (files).
But people have also imagined these structures growing down. In the early 1970's, I worked on a revolutionary computer operating system (a little TOO revolutionary, it never saw the light of day). The disk folder that contained all the other folders was not called the root, but rather, the "great directory in the sky." (By the way, that's a phrase that gets NO matches at all in a Google search.) And all the other folders and files branched downward from the sky. you see.
It's interestng how I managed to remember that name, "great directory in the sky," all these years. What really comes to mind is not the name, but its "mangle." This revolutionary operating system was compiled by a "pre-compiler" that turned its elegant source code into another language that a computer of the time could understand. That second compiler understood symbols as long as six characters, no more.
Many computer development systems support the ability to write symbols that are too long for other parts of their computer world to understand. These development systems "mangle" symbols, replacing the long ones by short enough symbols that are unique. For example, you might write a program with these symbols: forward_balance, forward_balance_estimated. If these symbols have to be represented by words only eight character long, they might be "mangled" into: forwbal1, forwbal2. And the mangle of "great_directory_in_the_sky" was the memorable "gdits," pronounced guhDITS.
(You'll be amazed if you search the web for gdits. An don't miss Peter Grubbs' song, Ghost Dachsunds in the Sky, on lyrics on this page.)