Entertainment is something that allows people to get in a state of euphoria, to forget about all the problems they have. It is about releasing seratonin, dopamine and other chemicals that the brain was evolved to react deeply with. It often hits the themes that human minds were shaped to understand, like social backstabbing and murders.
The word is sometimes abbreviated to entmt, especially on fliers for industry news events or when short hand note taking is involved. It is also used to refer to the act of entertaining, and to something affording pleasure, diversion or amusement, such as a performance.