Stories within novels are often referred to as subplots.
Subplots are the secondary plots which tell about the supporting part of the story. Often the supporting characters and themes are the part of the subplots. They add to the main plot of the novel to enhance the story and the important characters. Subplots rescue a novel to be monotonous in its approach through additional characters, themes, and plotlines.
A novella is a piece of literary work which is longer than a short story and shorter than a novel. There are fewer characters, conflicts, and complications in a Novella as compared to a Novel. But is much complex than a short story.
When a book or a group of events is divided into smaller fragments, it is known as chapters. Each chapter focuses on a certain topic with an end.
An incident or a part of the sequence is called an episode.
