Responsive web design (RWD) is a web design approach aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from mobile phones to desktop computer monitors).
As Smartphone and tablet adoption rapidly increases, so does the importance of mobile-friendly websites, one of the most appealing aspects of responsive web design is that a responsive website can provide a great user-experience across many devices and screen sizes. This is an important characteristic, since it is impossible to anticipate all the devices and screen sizes searchers will use to access your site. A site that works well regardless of these variables will provide a better and more consistent user-experience than a separate mobile site that is designed for a specific device and screen size.