Diameter Posted on 7th November 201528th August 2020 by ThePD (The Project Definition) A Diameter is a straight line going through the centre of a circle connecting two points on the circumference. 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 length, property. 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.