For me a new concept, but actually sounded very familiar and easy to understand, since I believe no matter what you do or like, at some point in your life, you must have felt in a state of "Flow".
So, what is it? Well, the "Flow" also known as "the zone" is the operating mental state in which a person is completely immersed in the activity that she or he executes. It is characterized by a feeling of focusing the energy, of total involvement with the task, and of success in carrying out the activity. This sensation is experienced while the activity is ongoing.
In this state you kind of separate from your body, you forget about your problems, about time and even your physical needs....it is like you are on a state of ecstasy... sounds familiar?
So basically, as you can see in the diagram, we can be in different states as we do an activity, depending on how much challenging this task is for us and how much of our skills is demanded.
The cenit would be the state of flow, is where we are more happy, excited and focused. The states of Arousal and Control are positive also, but the state of Apathy is the one we must avoid, is a state of sadness and depression.
Now, for some people is clear which activities make them FLOW, and for the rest of us, let`s hope we find them soon enough ;)