Entertaiment means the enjoyment of an activity. It can involve a range of activities from watching a performance to playing games.
The entertainment industry is based on the idea of giving people a break from the realities of life and transporting them into a different world. It also hits on themes the brain was evolved to react deeply to, like social backstabbing and murders.
One of the classic examples is Scheherazade, a story in the Persian professional storytelling tradition that has inspired multiple orchestral works, film adaptations and innovative video games. But the question of whether this kind of entertaiment is good or bad depends on how you look at it.