Responsive webdesign is the most important trend in 2012 in webdesign technologies. But why. Let’s start just basic:

Responsive means a flexible design self modifiing dependant on the final device. It is designed in HTML/CSS/Javascript and shows only useful layouts depending on the selected design.

So finally the pages should look better in all kinds of design.

A book apart already made a book out of this technology: http://www.abookapart.com/products/responsive-web-design/