In case you hadn't noticed, the V1.0 edition of the Horizon Wars: Zero Dark FAQ & Errata document has been published (FREE) on Wargame Vault.
Typically, though, I did forget one. I'll update the document eventually, but there has been a question asked - appropriately enough - frequently that I forgot to answer: What is "Def" for?
So I'll answer it here, now:
In the core rules, when shooting at a target with a Def stat, you add the Def to the range. Simples. It will have some other functions in due course but, for now, that's it.