Master pages in web development are used to develop a template, which is inherited by webpages to follow the same design theme and to share the common and global functionality.
You can add more master pages as required in the highlighted section. M# creates two types of master pages when a new project is created in M#. One is used to develop “Standard” pages and the other is used to develop “Modal / popup” pages which are discussed in another lesson of this chapter.
For more information on creating pages please read lesson Entities, page, module in chapter 1.