Flow comes from the research of the Hungarian turned American pyschologist, Mihaly Csikszentmihalyi. He did a study in the eighties (I think) in which he gave some people a pager that would go off at random intervals, prompting them to write down what they were doing and feeling at the time.
The findings are intuitive, but instructive to see in words: when the challenge of the activity is low you may feel apathetic, bored, or relaxed depending upon your skill level. When the challenge is moderate you probably feel either worried or in-control depending upon your skill level. When the challenge is high, emotions vary from anxious, aroused, or "flow". Learning tends to occur in the state of arousal. Meaning tends to occur in the state of flow.
So flow is a state we enter into in which our perceptions become absorbed by the task at hand. You might call it active engagement or being in the zone. When we enter this state time almost stops, our emotions cease, our whole being becomes absorbed in the task, we don't worry about failure, and we enter into a feed-back loop. This is a meaningful state to enter into everyday; so much so, that when flow is removed from people's lifes they tend to become irriatated, lethargic, and depressed.
So what does this mean for me as a worker? What does it mean for me as a teacher? As a husband, father, friend, stranger, human? Well it feels like I should try to increase the amount of time I spend in flow, but I should also try to increase the amounts of time I spend in arousal, control, and relaxation as well. When I am bored, it is probably because the challenge or my skills are too low - increase the challenge and move into arousal then get to flow as my skills increase, or simply increase my skills and move into relaxation. Alternatively I might just avoid that activity.
This idea of flow challenges me (and you) to improve my skills through arousal (or despite boredom) so that I can experience positive states of engagement more frequently and thus improve my well-being and enjoyment of life. It also suggests that I should remove or avoid the activities that cause me apathy, worry, or anxiety when possible. When I can't remove the activity or challenge, the solution is clear: IMPROVE.
Read Flow by Mihaly Csikszentmihalyi.