This level of architecture is defined in the common approach to Federal Enterprise Architecture Framework and focuses on a particular service area or business unit within an agency or between agencies that is not Federal-, Sector-, or Agency-wide. Each segment is defined either organizationally (e.g., as a business unit and per the organization chart) or functionally (as a vertical or crosscutting mission or support service).

Source: See Federal Enterprise Architecture Framework (common approach - as explained in Collaborative Planning Methodology).