High Design typically refers to products that start to cross over into the art zone. Typically they are extremely low tech, made from high intrinsic value materials, and wildly impractical.
An example of high design would be the Marc Newson bookcases that are cut from a single piece of Italian marble. The marble itself is incredible expensive, now cut most of it away and throw it out as waste, and you have an incredibly heavy shel that holds a few books all askew, but its main function is beauty, presence, and status. If you just wanted to hold books you would buy a Förgęnmoof or whatever from Ikea! 
