Here is the most accurate, but more importantly the most enabling, explanation of screenwriting I have ever seen or heard:
A film or motion picture is a series of moving pictures and sounds, designed and organized in a specific way to tell a story. A screenplay is architecture, not literature. The value of a screenplay is measured more by its construction than by the words on the page. —Tony Savant, leading Hollywood teacher, reviewer, and screenwriter
Think about it. In each “performance” of a novel (each reading) you have only one element (the words on a page) and two main participants:  the author and the reader. In a film (as you see in credits), it is a long list of people who come together to each play a part in making the film come alive and capturing it for presentation. A bad screenplay may spell out a good plot, but it may not contain the series of moving pictures and sounds, designed and organized in a specific way that achieve presenting the good plot effectively for a movie. A bad screen play may “over-specify” elements of the movie that constrain the film’s production so that it is cost-prohibitive in any number of ways. Or it maybe simply too disjointed when presented visually. A good screenplay enables the creative and production teams do their part, and provides “just enough framework” to enable them to create the “series of moving pictures and sounds” that are “designed and organized” to so that the teams to do their part and create a visual/audio story that is true to the original story and its plot. And it must provide a framework that above all achieves this: a story that touches the heart. The secret is to enable a film production that allows all the participants to contribute from their hearts. Heart crosses language and cultural barriers, and brings us together regardless of our backgrounds and experiences. It is the common touch point that allows the directors, cast, and production teams to see and feel exactly how to apply their own creativity to bring the work’s vision to life. The screenplay has to provide just enough framework to enable, but not constrain. So in my screenwriting, as I write each word and each line, I envision how each of the creative participants could contribute from their heart. To “put their all” into the work, whether big or small. Whether it is an action story, a romance, or the plight or success of a fellow human being from today’s world or history—it has to stir our heart in one way or another. That’s what makes good screenwriting a challenge, but it’s a challenge I love.