Responsive web design (also known as 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 desktop computer monitors to mobile phones).

Responsive web design (RWD) means that you don't need to have separate PC, laptop, tablet and mobile versions of your website. The site adapts to whatever size screen it's being displayed on. Despite of what device a visitor is using to access your site, they will see all of the content you have to offer (no more partial-content mobile versions of sites) and they'll see it in readable way.