https://docs.servicenow.com/bundle/rome-platform-user-interface/page/administer/navigation-and-ui/task
/t_CreateAModule.html
A module is the functionality within an application menu such as opening a page in the content frame or a separate tab or window. For example, Open is a module under the Problem application menu that opens a list of problem records. Modules are the second level navigation options for applications. Reference: Modules | ServiceNow Tutorials