The actual definition of fun:
Recreation, play, and fun are not the preserve of humans; nearly all creatures indulge in this to some extent. Play is essential for the development of skills, the most basic of which are motor skills in young creatures.
The choice of hours for recreation is, for employees, restricted by the requirements of, and agreements with, the employer (working time), and for students by school hours. For people with their own business it is also restricted by the requirements of the work, such as the opening hours of the business based on wishes of customers, laws, and customs.
The weekend is usually a time for recreation, perhaps (in Judeo-Christian and Muslim cultures) because the Sabbath falls on the weekend and the Sabbath is "the day of rest." Holidays are also a common time for recreation, though recreation may take place at virtually any time. Recreation commonly occurs during an individual's discretionary time.
Traditionally olympics music and dance serve as recreation in many cultures, as do sports, hobbies, games (playing) and tourism. Watching TV and listening to music are common forms of recreation, or rather leisure.
Wikipedia has it all. Amazing.