What is Responsive Web Design?

Responsive web design (RWD) is an approach to web design that makes web pages render well on a variety of devices and window or screen sizes. Recent work also considers the viewer proximity as part of the viewing context as an extension for RWD. Content, design and performance are necessary across all devices to ensure usability and satisfaction. Responsive sites check the size of the device and adjust themselves automatically to fit.
Responsive web design has become more important as the amount of mobile traffic now accounts for more than half of total internet traffic.