Описание тега adaptive-design

Adaptive design uses a server side, predefined set of layouts and appearances based on the user's preferences and platform on which they are viewing content to style the page. While this is very similar to responsive design in that it attempts to set up responsive structures for new devices, this varies from responsive design through the delivery of the responsive structures. Adaptive design relies more heavily on predefined screen sizes and less on fluid foundations.

Often times adaptive design is faster and allows certain platforms to be heavily optimized for maximum presentation compared to responsive design, but lacks when variations from the predefined layouts occur. Adaptive design is more fluid and responds easier to every platform but is generally slower to load and requires that the designer know how to make their content dependent on the user's device and specifications.

For a full analysis of this topic, check out this TechRepublic article, this Huffington Post article, or one of the many other articles comparing the two approaches