Well, Web Design and Web Development are NOT interchangeable terms, nor are they even close to being the same thing...despite what some may think.
In a nutshell... it's like this:
Web Design
The look of the site, what you see when you visit.
Web Designers:
- Study and put into practice Graphic Design principles like Typography, grid structures, hierarchy, color theory, etc.
- Create layouts for the site
- Create graphics for the site using Illustrator and Photoshop
- Collect and prepare images for the site
- Do minor coding with HTML and CSS
- Create site features with Flash
Web Development
The back end of things, what you don't see but still keeps the site going and what makes it work. Development requires lots of work with coding and little to do with how a site looks aesthetically.
Web Developers work with:
- Intermediate Markup languages such as XHTML and XML
- Advanced Style sheet languages in CSS and XSL
- Client-side scripting using JavaScript and VBScript
- Server-side scripting with PHP, Python, Ruby, JSP, .NET
- Databases using MySQL, ColdFusion
- Advanced ActionScripting with Flash
Designers and Developers usually work as a team, though not always.
Unless one is doubly skilled... it is fairly obvious when a Designer tries to develop and when a Developer tries to design.