Entertaiment is a broad term that can refer to a wide variety of events. It can involve amusement, such as a circus, a carnival, or a game of chance; it can also be serious, such as a religious festival, or a piece of satire. Entertainment often hits on themes that our brains were evolved to react deeply to, like social backstabbing and murders.
What is more interesting is that entertainment has the ability to cross media, enabling it to evolve and adapt to any scale from a one-on-one experience to a global audience. This gives it a unique quality that is highly durable.