the 2 popular Ds associated with a Webpany (Web Company), Webperty (Web Property), Weblog (Weblogs) and Web Sites are Development and Designing. The third D is Display. The term Display is not associated with how it is seen on a browser and mobile or how is the user interface, these comes in designing, rather it is associated with online marketing and promotion. The display of Web, needs other 2 Ds i.e. development and designing to have a better display.
What Display covers?
Display means promotion of web property using online means like SEO, SMO and SEM and for these other 2-Ds are also required and should go along with Display. For a better display i.e. better reach and engagement of web users one needs to optmise his web property with better URL links, headings, image alt text and social networking presence along with apps, gadgets and widgets. Again, other 2-Ds would be used in developing these gadgets and giving them a better look with designing, but it would be display that would make it reach to your audience.