What type of stories captures the overall purpose of an application?

The correct choice, which is themes, represents a high-level narrative that encapsulates the overall purpose and objectives of an application. Themes are broader than user stories and provide a strategic context for the development of features and functionalities within the application. They help to align the development team's work with the organization's goals and user needs, serving as guiding principles throughout the application's lifecycle.

Themes allow stakeholders to understand the primary motivations behind certain features, helping to prioritize and implement functional requirements that drive the necessary business outcomes. By focusing on themes, teams can ensure that all components of the application work harmoniously towards achieving the overarching vision.

In contrast, user stories are typically more specific, detailing individual needs of users without necessarily capturing the full scope or purpose of the entire application. Epics, while larger collections of related user stories, still operate at a lower level, concentrating on specific increments of functionality. Specifications are more technical documents that articulate requirements and design details rather than conveying the overarching goals or themes of the application. Thus, themes provide a comprehensive view necessary for guiding development towards fulfilling the core purpose of the application.