What Is Peace?

The kids have this little book by Todd Parr called "The Peace Book" and it got me to thinking. Peace is a positive concept, not defined simply as the absence of war. What else, then, is a necessary or sufficient condition for peace? I don't mean peace in terms of quiet or solitude, but as a social/political concept. When we say of a place that it is peaceful or when we say we are working for peace, what is it exactly that we are pointing to?