Responsive Web Design(RWD) is an web design aimed at allowing desktop webpages to be viewed in response to the size of the device one is viewing with.A site designed with RWD adaptts the layout to the viewing environments by using fluid, propotion-based grids, flexible images, and CSS3 media queries,an extension of the rule, in the following ways:

The fluid grid concept calls for page element sizing to be in relative units like percentages, rather than absolute units like pixels or points.

Flexible images are also sized in relative units,so as to prevents them from displaying outsides their containing elements.

Media queries allow the pages to use different CSS style rules based on characteristics of the device the site is being displayed on, most commonly the width of the browser.

Responsive web design has become more important as the amount of mobile traffic now accounts for more than half of totle internet traffic.