This feature is available in Ultimate edition only.
Strategic Themes are assets that reflect top-tier strategic planning activities at the company and/or organizational level. Product owners can use them to divide, group, and prioritize top-level portfolio items in a manner that reflects the targets and strategic priorities of the company. This helps keep the development plans aligned with the strategic priorities.
You can associate a portfolio item to more than one strategic theme to provide a birds-eye view across all products and see how you are progressing towards a specific top-level objective.