I understand the idea of a callback, where I pass a function into another function and that function then uses the supplied function at will.

I am struggling to understand deferred callbacks, even after googling it.

Could someone provide a simple explanation please? I program in Ruby, but also know C/C++ a bit, but most of all I was a experienced assembly language programmer. So I am wondering is it a bit like a stack of callback addresses that get pop'd? I am hoping to learn jquery or node.js and these deferred callbacks seem integral to both. I understand basic threading principles (though mutex object makes my head hurt ;)