The definition of compassion is the ability to understand the emotional state of another person or oneself. Often confused with empathy, compassion has the added element of having a desire to alleviate or reduce the suffering of another. Empathy, as most people know, is the ability to put oneself in the other person's place. Although compassion and empathy are two separate things, having compassion for someone can lead to feeling empathy for another person.
http://blogs.psychologytoday.com/blog/the-compassion-chronicles/200804/what-is-compassion-and-how-can-it-improve-my-life