Put very simply, a plot is what happens in a story. The quote above by author and former editor at Highlights For Children magazine says the same thing but far more eloquently.
When writing fiction or creative nonfiction, we want to grab the reader immediately. That's a given, isn't it? The hard part is to keep the reader wanting to turn the page. Once we have the reader ensnared, or should I say--captivated--it is up to us to hold on to that reader through the rest of the story. This goes for both novels and short stories.
When do we let go? When the story ends. We hope the reader finishes the last paragraph with satisfaction. My Book Club read a novel recently that pulled the reader into the story and kept them interested but the ending left us all saying "What?" It proved more frustrating than satisfying. I've recommended a book by Nancy Kress titled Beginnings, Middles and Ends. If she can write fully one-third of a book on the endings of our stories, they must be pretty important. Your library may have a copy of this reference book for writers or you can order it on Amazon at the link above.
It's your job as a writer to keep the reader engaged. I'm reading a book right now that made me want to quit in the first fifty pages, but then the story started pulling me in and I am picking up the book whenever I have some spare minutes to read. I managed to stay with the novel until it did capture my interest but many times a reader will slam the books closed and move on to another. This author is doing a good job after establishing the situation in those first fifty pages which tended to repeat the same information instead of moving on at a swift pace. The author didn't grab the reader in the beginning so she might lose many readers before the real story begins.
It's tough work pulling a reader into a story and keeping them. Chapters need to end with some reason for the reader to want to go on to the next one. We've all read reviews of books that tell us the author had enough plot twists and turns to keep the reader enthralled and reading rapidly. That doesn't just happen. The writer must structure the story very carefully.
Whether defined with simple words or eloquent ones, what happens in a story is like clay in the hands of a sculptor. It's nothing at first but can evolve into a fine piece of art, or in this case, literature.