Responsive design is a way to put together a website so that it automatically scales it’s content and elements to match the screen size on which it is viewed. It keeps images from being larger than the screen width, and prevents visitors on mobile devices from needing to do extra work to read your content.
The ultimate goal of responsive design it to avoid the unnecessary resizing, scrolling, zooming or panning that occurs with sites that have not been optimized for different devices. It is often very difficult to navigate these sites and it may even cost you a potential customer who becomes frustrated with trying to figure out how to work the website.
Responsive website design also replaces the previous need to design a dedicated mobile website for smartphone users. Now, instead of designing multiple websites for different screen sizes you can design just one website that scales up or down automatically to match the device it’s being viewed on.