Muditā (Pāli and Sanskrit: मुदिता) means joy; especially sympathetic or vicarious joy.
Also: the pleasure that comes from delighting in other people’s well-being.
The traditional paradigmatic example of this mind-state is the attitude of a parent observing a growing child’s accomplishments and successes. Mudita should not be confused with pride, as a person feeling mudita may not have any interest or direct income from the accomplishments of the other. Mudita is a pure joy unadulterated by self-interest.
When we can be happy of the joys other beings feel, it is called mudita; the opposite word is invidia.
(Content above from Mudita Wikipedia page)