Jamie Zawinski uses that term in his (1997) article "java sucks" as if you should know what it means:

I really hate the lack of downward-funargs; anonymous classes are a lame substitute. (I can live without long-lived closures, but I find lack of function pointers a huge pain.)

It seems to be Lisper's slang, and I could find the following brief definition here, but somehow, I think I still don't get it:

Many closures are used only during the extent of the bindings they refer to; these are known as "downward funargs" in Lisp parlance.

Were it not for Steve Yegge, I'd just feel stupid now, but it seems, it might be OK to ask:

Jamie Zawinski is a hero. A living legend. [...] A guy who can use the term "downward funargs" and then glare at you just daring you to ask him to explain it, you cretin. -- XEmacs is dead, long live XEmacs

So is there a Lisper here who can compile this for C-style-programmers like me?