Responsive web design definition

Responsive web design (RWD) is a web development approach that creates dynamic changes to the appearance of a website, depending on the screen size and orientation of the device being used to view it. RWD is one approach to the problem of designing for the multitude of devices available to customers, ranging from tiny phones to huge desktop monitors.

RWD uses so-called breakpoints to determine how the layout of a site will appear: one design is used above a breakpoints and another design is applied below that breakpoints. The breakpoints are commonly based on the width of the browser.