Here is one definition of Zen:

"True Zen consists of sitting quietly in the correct posture. It is not a special state, it is the normal state: silent, peaceful, without agitation. Zen means to put the mind at rest and to concentrate the mind and body. In zazen there is no purpose, no seeking to gain something, no special effort or imagination. It is not knowledge to be grasped by the brain. It is solely a practice, a practice which is the true gate to happiness, peace and freedom."

~ Taisen Deshimaru Roshi

Wow, that really resonates with me today.