As a former athlete, and a parent of athletes I understand the concept of being in the "Zone". The Zone of Optimal Functioning in sports psychology synthesizes that an athlete will perform best within a zone of optimal arousal. This zone applies to multiple psychological variables including cognitive anxiety and somatic anxiety. The cognitive anxiety refers to the negative expectations and the mental worries about ones performance in a competitive situation. Somatic anxiety deals with self-perception of physiological arousal which involves nervousness and tension. I have watched my children perform in high level competitions, and you can tell when they are in the "Zone", the moment when everything comes together and they achieve their best performance. It is like a release of a positive energy. My daughter would prepare herself by focusing and putting on her game face before race, you knew she was focused and ready for the competition. My son, a pitcher, prepares himself quite differently. He acts like it is just another ordinary moment in life, even when he is on the mound, he seems very loose. Both of my children are competitors, but they operate and function in different zones. My daughter allows the tension to build and then a quick release, and my son seems to go with the flow with less tension and anxiety. This could be due to the nature of the events, where my daughter was a short distant sprinter in swimming, and the event required a burst of energy. Where as a pitcher needs to remain more constant and composed.
The "Zone" does not just apply to athletics, but it can be seen in other life events. If a musical performance is required the musician wants to be in their "Zone". I think in any life situation where one is required to perform some type of task where they will be judged by others there is a level of optimal performance that we want to achieve, and to achieve that optimal performance, one needs to be in their "Zone".
Here is a short video of world premier golfer talking about when he knew he was in his "Zone", everything came together for him on that day in that moment.