What is FUN? on the psychological “Flow” Effect or State

On the importance of “Flow” in work environments you might ask… WHAT IS FLOW ?

The psychological state of effortlessness, where you become completely absorbs and time seems to FLY BY is flow.

Asking Google for a definition you just get crap… Google Search: define:flow

FLOW is a psychological theory from the late 80s by a guy called Mihaly Csikszentmihalyi that you can or buy at Amazon or [at this book store][2]

The question he posed himself was simple: What is fun? What makes some experiences enjoyable, and other experiences not?

For a brief overview I also found a very nice essay that copes with the personal experience and influence that the book had on the author.