A clown at a birthday party, a Broadway show, a stadium rock concert, or just your friends fighting over the last potato chip are all forms of entertainment. It comes from the Old French word entretenir, meaning support or hold together, and was used in a hospitable sense for entertaining guests. Today it is often used to mean amusement or distraction, and you might see it abbreviated as entmt on a flier or in industry news where space is limited.
The best forms of entertainment hit on the points that our brains were evolved to deeply react to in order to understand the world around us. This can be humor, backstabbing and murders and it can also be art, satire, or other themes that require higher level thinking to fully appreciate.