The Focus Point is the value used to tell the device where a user’s focus is. This defines a plane that is used to increase hologram quality for content that intersects the plane. Use the FocusPoint API to define this plane, to help stabilize the most important content currently in the user’s view. The FocusPoint API can be found in HolographicSettings.SetFocusPointForFrame.
For more information about how the HoloLens achieves stable holograms, see Microsoft’s documentation on Hologram stability.