As my aunt Sally would say; "Gosh Darn!", why do you ask such obtuse questions;...

"I don't like that nebulous term backlog either.  What does that mean EXACTLY?"...

Here is the NEW WORLD DICTIONARY's relevant statement as to what is meant by the word "back log"...

"3. An accumulation of unfilled orders, unfinished work, etc."...

Capeesh?...Lol...Lol...

Gil...