Definition - What does Mudita mean?
Mudita is a Sanskrit term that means "joy" or "pleasure." It refers to the kind of pleasure that can be obtained from seeing other people do well.
Mudita is commonly explained by comparing it to the joy and satisfaction a parent gets from watching their child grow up and become successful.
Yogapedia explains Mudita
It is important to remember that mudita is a pure kind of pleasure which is gained from another's accomplishments without any form of self-interest involved. This concept is used in the practice of Mudita meditation. By practicing this meditation method, a yogi can learn to cultivate joy at the good things which happen to other humans.
Mudita is taught in Buddhism as a way of gaining an inner source of infinite joy which can always be accessed and enjoyed. While this kind of empathetic joy is seen as being the most difficult of the brahmavihara (four sublime attitudes) to achieve, it can greatly enhance the life of anyone who achieves it.