The mental state of being fully immersed in an activity, characterized by intense focus, loss of time perception, and intrinsic enjoyment in the process of the activity.
Characteristics of flow:
Sense of time is distorted
Intense and focused concentration on the present moment and task at hand
Loss of reflective self-consciousness where other needs become negligible - distractions are excluded from consciousness and there is no worry of failure
Experience of the immediate activity is intrinsically rewarding and becomes an end in itself
Strong sense of personal control or agency over the situation or activity
What is required to enter flow:
Flow requires balance between challenge and skill level
Clear goals and progress with immediate and unambiguous feedback - there is knowledge of how to proceed and a strong sense of potential to succeed
Autotelicity - i.e. intrinsic motivation in an activity for its own sake
References
Flow: The Psychology of Optimal Experience by Mihaly Csikszentmihalyi