Entertaiment is any form of entertainment that can be consumed and provides a positive experience for the audience. Bates and Ferri (2010) define it as an activity that is understood objectively, involves communication between text and audience from an external stimulus, offers pleasure, requires an audience to exist and occurs in a passive form. Entertainment also stimulates the brain to realease seratonin and other chemicals, because it often hits on points that the human mind was evolved to deeply react to in a social world.
You may see the word Entertaiment abbreviated to entmt on fliers or in industry news publications, but it is not commonly abbreviated in general prose.