Entertaiment means something to amuse or divert the mind. It can be a hobby, like solving crossword puzzles or playing games, or entertainment in the form of sports or performances.
Entertaiment hits on the deep emotions that our brains were evolved to react to in order to help us understand the world around us. It can be fun, exciting and even dangerous at times. It can also stimulate the release of seratonin and dopamine. It can be a form of therapy as well.
It is sometimes abbreviated to entmt on fliers and in industry news publications for short hand note taking. This word is derived from the French term entretenement. Other interesting words are entretenance, entrainment and entretenoire.