Some of the time, the terms 'web design' and 'web development' are used interchangeably, but the two phrases actually mean two different things. So that you don't get stuck with a service you didn't sign up for, I will go through the two terms and describe them thoroughly.

The Definition of Web Design

Web design typically refers to the process of designing a web site or web page layout and often includes the graphical elements on a page. The design can be developed using a graphics program such as Adobe Photoshop, and provides the framework for the look and feel of a web page. - Source - impliedbydesign.com

The finished product of the design does not typically contain code. Rather, the graphical representation of the web page is used by another or the same party as the basis for the code. The representation is divided into areas that can be represented by web code, and other areas that are purely graphics.

Often, web design and development firms use the term 'web design' to refer to the entire development of a web site because it is the most commonly recognized term in the marketplace. However, it is important to clarify what a firm means before signing up for their 'web design' services.

The Definition of Web Development

Web development is typically used to described the programming required to construct the 'back end' of a website. The back end is the area of the site that isn't seen by visitors, but which does the work required in order to present the right information in the correct format to the visitors.- Source - impliedbydesign.com

Web development is used to describe any database-driven web designs using dynamic scripting languages like PHP, ASP, ASP.NET and Coldfusion. It also covers database design and development. The term can also be used for client-side scripting such as JavaScript and Java.