what is the name for the space between the leaves of a tree I am trying to write a data-type not for a tree, but for the spaces in between the leaves of thee tree.  In number theory (a part of math) this is known as a topograph does it have a name in CS?
The empty space is called "OTIOSE".   Pronounced "oh-she-ohs"

otiosity

Synonyms &amp; Antonyms for otiose 
Synonyms
abortive, barren, bootless, empty, fruitless, futile, ineffective, ineffectual, inefficacious, profitless, unavailing, unproductive, unprofitable, unsuccessful, useless, vain