By request, here are comments presented as an answer:
I'm not sure you completely grok the fact that functions in JS are first-class objects, and can therefore be stored until needed, past the time they are created.
For example, say you want to write to a file, then print out a log message; so you call the "write()" function (or whatever) and pass it a function that outputs the log message (this is the deferred callback function). "write()" internally stores a reference to the given function, starts writing to the file, and sets up its own callback to know when the write is finished. It then returns before the write is done; when it is, the internal callback is somehow called (this is the underlying framework's job -- in the case of node.js, it's done with an event loop), which then calls your callback which prints the log message.
The "deferred" part simply means that your callback function isn't called right away; calling it is deferred until the appropriate time. In the case of asynchronous functions like many of those in node.js, the given callback is generally called when the operation completes (or an error occurs).
The fact that the underlying system is event-driven is orthogonal to the use of deferred callbacks; you can imagine a (very slow) version of node.js that started a thread for every operation, and then called your given callback when the thread finished its work, without using events at all. Of course, this is a horrible model, but it illustrates my point :-)
Deferredobjects? Is is this about something specific to Node.js?