Flow is not a buzzword. The concept of flow was introduced by Mihaly Csikszentmihalyi in his book Flow: The Psychology of Optimal Experience. It is a known concept in psychology.
It is achieved when skill level is high and challenge level is high.
http://en.wikipedia.org/wiki/Flow_%28psychology%29
Flow is the mental state of operation in which a person performing an activity is fully immersed in a feeling of energized focus, full involvement, and enjoyment in the process of the activity. In essence, flow is characterized by complete absorption in what one does. Proposed by Mihály Csíkszentmihályi, this positive psychology concept has been widely referenced across a variety of fields.
Flow theory postulates three conditions that have to be met to achieve a flow state:
One must be involved in an activity with a clear set of goals and progress. This adds direction and structure to the task.[11]
The task at hand must have clear and immediate feedback. This helps the person negotiate any changing demands and allows him or her to adjust his or her performance to maintain the flow state.[11]
One must have a good balance between the perceived challenges of the task at hand and his or her own perceived skills. One must have confidence that he or she is capable to do the task at hand.[11]
However, it was argued that the antecedent factors of flow are interrelated, as a perceived balance between challenges and skills requires that one knows what he or she has to do (clear goals) and how successful he or she is in doing it (immediate feedback). Thus, a perceived fit of skills and task demands can be identified as the central precondition of flow experiences.[12]