An “adaptation” is a type of derivate work that takes specific elements from a previously created work, in any given media format, and utilizes them in a different media format. The recycling of a concept from one media to another, is part of what this site is all about.
For example, French author Pierre Boulle wrote a novel called “La Planete des singes”, that was first published in 1963. The English translation is “Planet of the Apes”, which became a theatrical motion picture in 1968. The now famous movie staring Charlton Heston had been adapted from the book written five years earlier. Although a great deal of the story had been changed, the basic premise remained the same, and characters from the novel were featured in the movie.
Novels have always been a prime source for movie material, especially in the early days of cinema. In 1924, filmaker Erich von Stroheim released a silent film entitled “Greed”, that was an apaptation of a Frank Norris’s novel “McTeauge”. Stroheim attempted to include every facet of the novel, and the film was over sixteen hours long. Not many film directors since then have tried to do such literal translations when adapting a novel into a movie. Therefore, a lot of content is usually altered and omitted to fit the parameters of the film media.
When the adaptive process goes in the other direction, the resulting book written from a movie is usually called a novelization. Novelizations will usually expand upon or add content to take full advantage of their storytelling format. So, novels get adapted into movies, and movies get adapted into novels, but that’s not all. Movies get adapted into television shows, television shows get adapted into movies, video games get adapted into cartoons, cartoons get adapted into…well, I think the point has been made. If something is popular in one media, it might be popular in another.