Wireframes describe the basic elements of a site that define structure, page layout, and the interaction flow from page to page. Wireframes are sketches, "frames of wire," that can be created when the basic idea about a site's purpose, users and content are known. The main purpose of a wireframe is to define the skeleton of the page and not the graphical design of it. Most wireframes are grayscale designed web pages with labeled boxes.

The main advantage of wireframes is that all elements are easy to change and many iterations can be done in a short time, which can save the design team time. The entire site and all of its interaction aspects can be evaluated before any graphical design or programming is done. The design team can see how the navigation and grouping works and check whether the important elements are located in the right spots. Some of the rough wireframes can even be used to test with the end users.

References:

1) Wireframes- The Web’s Best Design Technique. Web Administration: University of Florida.
Retrieved from: http://www.webadmin.ufl.edu/wpm/wireframes.pdf

2) Wireframes. IAwiki.
Retrieved from: http://www.iawiki.net/WireFrames