In short, responsive web design can be defined as one website for multiple screens. What this means is: gone are the days of having to create a separate mobile website. Now you can create a responsive website that will fit all screens on all devices from desktop computers to mobile phones. Responsive websites look better on mobile devices and are thus more user-friendly.
According to Google’s Webmaster Central Blog, “The change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Consequently, users will find it easier to get relevant, high quality search results that are optimized for their devices.”