Responsive web design (RWD) is an approach to web design aimed at allowing desktop webpages to be viewed in response to the size of the screen or web browser one is viewing with.
A site designed with RWD adapts the layout to the viewing environment by using fluid, proportion-based grids, flexible images, and CSS3 media queries.
Responsive web design has become more important as the amount of mobile traffic now accounts for more than half of total internet traffic.
Google’s Mobilegeddon was rolled out in 2015 and is in full swing now. This means is if your website is still not mobile ready it will be ranked lower on mobile devices. Your site could be on page 1 of a desktop search but page 3 on a phone. Not good.
Responsive Website Design vs. Mobile Design