Entertaiment is a broad and evolving field. It can range from a single individual selecting their own entertainment on TV or in a theatre, to an entire family celebrating at home with food, music and dance, to a seated audience attending a performance — or even global audiences enjoying an online movie or game. It may be amusing, but it can also serve a more serious purpose such as providing insight or a sense of intellectual growth. The power of entertainment is demonstrated in the way that stories such as Scheherazade, in the Persian professional storytelling tradition, inspire a variety of forms from orchestral music to film and video games.
You may see the word entertainment abbreviated to entmt on a flier or in industry news publications where space is limited. But in general, this is not an abbreviation you will encounter outside of those contexts.