Definition of PEACE for Kids. 1. : freedom or a period of freedom from public disturbance or war. 2. : a quiet and calm state of mind. 3. : agreement and harmony among people. 4. : an agreement to end a war. He tried to negotiate a peace between the warring countries. 2  There was a peace of 50 years before war broke out again. 3  Peace and order were finally restored in the town. 4  After years of therapy, he has finally achieved an inner peace.