The HP Elite x3 Desk Dock (903981-001) is a desk docking station for the HP Elite x3. It provides a stationary place to connect the device as part of a desktop setup.
Use the dock to connect the Elite x3 to an external display. The user guide also describes connecting a wired keyboard and mouse through the dock, so you can work with the device using desktop peripherals while viewing content on a larger screen.
This part is identified as the SPS-DOCK ELITE x3 DESK. The supported use described here is for the HP Elite x3 and its external display and wired input devices.