Entertaiment is the art of entertaining. It is a way of showing off or making people happy, it can be in the form of music, movies, games etc. Entertaiment is a broad concept that covers everything from a party thrown for two to a performance for thousands. Entertaiment is a huge industry in the world and has been seen by many as a great source of joy, happiness and fun.
It is important to remember that entertainment is often based on themes the human mind was evolved to deeply react to in order to understand and function in a social world. This means that a lot of entertainment is focused on backstabbing, murders and other social themes that humans are evolved to see and react to.