A state of psychological wellbeing and calmness within oneself despite the happenings of the world around you or as I'd like to call it the consistent pining or yearning for "true contentment".
The concept of peace is a tough one to grasp, how do you know you're truly at peace? What are the determining factors? Is peace the absence of conflict or the ability to work and live through it?
We constantly push ourselves and run our minds through the mill trying to achieve a goal that's relative. So set on an ideal of what contentment is and should be, we subject ourselves to more mental torture trying to attain what we feel and see as peace rather than figuring out what works for us. There can never be a process of betterment without taking yourself into account. Your peace could be in coming to terms with certain things rather than trying to change them, or changing your approach to life or even taking care of yourself more. You are your peace, it's up to you to find your space or flow.