This is a term invented by Alan Cooper in his seminal work The Essentials of Interaction Design (buy it; it's brilliant). A program that runs in sovereign posture takes over the user's screen, and provides a launch site for all the functions they require to complete a domain-specific task. The TWiki "view" screen is SovereignPosture, because it acts as a launchpad for other more TransientPosture applications, such as the "more settings" and "edit" screens.
See this article by Cooper describing the main application postures.
See also: TransientPosture, DaemonicPosture
-- Contributors:CrawfordCurrie - 22 Jul 2007