User-maintained pages allow users to add and maintain data, often referred to as reference data, because the data is referred to during transaction and batch processing. With the proper security authorization, one can add, change, and delete information in these pages. These pages are used to define transaction processing rules, system options, security, batch defaults, and valid values (often called codes) that can be used on transactions, as well as other user-maintained pages.
Documentation in the many other users guides will point out what user-maintained pages are to be setup in each area of the application. Please see those guides for more information on this type of page data.