Responsive web design
Sometimes abbreviated as RWD, responsive web design is method of creating webpages so that they adjust based on the device they're viewed on. For example, when a user views a website on a desktop computer, they often have a large screen with 12 to 18 point font. However, when this same site is viewed from a smartphone or tablet, it is scaled down. Even though the screen may be a bit closer, the content is much smaller; therefore it would need to be adjusted so that the user could have a better browsing experience.
How does it work?
Responsive web design works by using percentage measurements for their HTML elements so that they may scale appropriately, rather than fixed measurements like the points or pixels traditionally used on desktop-only websites. Additionally, the @media rule is used to call special CSS settings based on the device; usually depending on the width of the browser.