Responsive web design is a web design technology approach aimed at programming sites that provide an optimal viewing experience – easy reading and navigation, with a minimum of resizing, panning and scrolling, across a wide range of devices such as mobile phones, tablets and desktop monitors.
In 2010, a brilliant guy named Ethan Marcotte decided to challenge the existing approach to web design by proposing to use the same content, but different layouts for the design, and coined the term Responsive Web Design. Technically we still use HTML and CSS, so it is rather a conceptual advancement. For a designer, responsive means mocking up multiple layouts. For the client, it means it works on the phone. For a developer, it is the way images are served, download speeds, semantics, mobile/desktop first and more. The main benefit here is the content parity, meaning that it’s the same website that works everywhere.