Series list refers to a series of titles or works that are related to each other in some way. It could include different books, movies, video games, TV shows, and so on.
For example, the Harry Potter series includes all seven books, the movies, and any spin offs or related material. Similarly, the Game of Thrones book series includes the main five titles, plus several related books and materials.
A series list is often differentiated from a franchise, which may contain multiple titles in multiple media, as well as related materials and even spin offs. A good example of this is the Star Wars franchise, which includes the original movies, prequels, sequels, several animated series, comic books, trading cards, and much more.
Generally, series lists are helpful for organizing and cataloging the different titles and materials related to a set of works. It can be easier to have them all laid out in one place instead of searching through several sources.