Responsive website design (RWD) allows users to pull up the same website from different devices that have different sized screens and still retain the functionality of the site regardless of the size of the screen. The responsive aspect will make the page display less information on smaller screens but not lose the information that is not on show as compared to a full screen site view. It allows the layout to the viewing environment to be adapted through using fluid, proportion based grids, CSS media queries and flexible images.
The importance of responsive website design is increasing in line with the amount of mobile devices on the market and the fact that many now view websites through their mobile devices. RWD is also known as a function of user interface.