A Wireframe is much easier to adapt than a Concept Design
It is quicker and cheaper to review and amend the structure of the key pages in a wireframe format. Iterating the development of the wireframes to a final version will provide the client and the design team confidence that the page is catering to user needs whilst fulfilling the key business and project objectives.
Often used to complete the User Centered Design process, wireframes are also used at the beginning of the design phase. A prototype usability test will often be a test of the wireframe pages to provide user feedback prior to the creative process.
Wireframes can be simply hand drawn, but are often put together using software like Microsoft’s Visio, to provide an on-screen delivery.
However, if the wireframes are going to be used for a prototype usability test, it is best to create them in HTML. There is some good software that allows you to do this easily including Axure RP or Omnigraffle (Mac only).