Which psychological word describes this situation best? A few years ago, I’ve heard that people have to be in the center if they want to truly enjoy something. For example, when someone really want to enjoy a concert, he or she needs to go to the center of the crowd. It is also true when you work.

Is there any psychological terminology or effect which describes this situation well?

Thank you.
Maybe you mean an engagement?
If though, a positive psychology have term flow state - when you fully immersed. Here is wiki article about it. Or hyperfocus - article.

Components of flow state:

Intense and focused concentration on the present moment

Merging of action and awareness

A loss of reflective self-consciousness

A sense of personal control or agency over the situation or activity

A distortion of temporal experience, one's subjective experience of time is altered

Experience of the activity as intrinsically rewarding, also referred to as autotelicexperience