A website with a responsive design is one that changes its layout according to the size of the device it’s being viewed on by each user. Whether the site is being viewed on a desktop, laptop, tablet or smart phone, it reformats itself to align with the different screen size so that its appearance is always optimized.
This means you don’t need to have separate mobile-optimized websites with different URLs and duplicate pages. A responsive website presents the same content on tablets and smart phones as it displays on computers.