Short answers, pulled from the story.
Entertainment is a form of activity that holds the attention and interest of an audience or gives pleasure and delight. It can be an idea or a task, but it is more commonly one of the activities or events developed over thousands of years to engage an audience.
The audience is the key aspect that transforms a private recreation or leisure activity into entertainment. The audience may have a passive role, as when watching a play or film, or an active role, as in games where participant and audience roles can interchange.
The Oxford English Dictionary gives Latin and French origins for entertain, including inter, meaning among, and tenir, meaning to hold, giving the sense to hold mutually or to hold intertwined. It cites a usage from 1490 by William Caxton.
Psychologists say the function of media entertainment is the attainment of gratification, with no other measurable benefit usually expected. Education is designed to develop understanding, and marketing aims to encourage people to buy products, though the distinctions blur in edutainment and infotainment.
Blood sports such as bear-baiting, dog fighting, and cockfighting have become illegal because of the cruelty involved. Public punishment as entertainment, including public hangings, lasted until the 19th century before writers and philosophers condemned it.
Technological developments in the 20th century, especially in mass media, meant entertainment could be produced independently of the audience, packaged, and sold on a commercial basis. Sometimes called show business, the industry became so sophisticated that its economics became a separate area of academic study.