System files - SystemTheme.qxtheme, SystemTheme.css, SystemActionDefaults.fm2, and SystemResources.tr2 - are global configuration files that specify basic parameters of all applications developed, deployed, and run via Lycia.

Master files - master theme, master css style, master action defaults file, and master resource file - share the name with the 4gl program, are loaded automatically when it is run and are used to secure its unique appearance and behavior as compared to other applications developed for the same company.

User files - user theme, user css style, and user action defaults file - are user-defined files that are loaded from the 4gl code and are mostly used for changing its runtime appearance and behavior depending on the current tasks and purposes.

For more details, refer to the respective pages of such files.