There are many definitions, some long, some short, but these are our favorite definitions of Calm, Zen and Mindfulness.
Calm is tranquility. (www.dictionary.com)
Zen is a way of being. It also is a state of mind. Zen involves dropping illusion and seeing things without distortion created by your own thoughts.
www.urbandictionary.com
Mindfulness is a technique in which one focuses one's full attention only on the present, experiencing thoughts, feelings, and sensations but not judging them. www.dictionary.com