Back Flow Posted on 3rd November 201522nd October 2020 by ThePD (The Project Definition) Back Flow is a flowing back or returning in the reverse direction, toward a source. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in Engineering and tagged engineering, process. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.