Defining Responsive Design by Neilson Norman – “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.”
Also described in Techtarget – “Responsive design is an approach to web page creation that makes use of flexible layouts, flexible images and cascading style sheet media queries. The goal of responsive design is to build web pages that detect the visitor’s screen size and orientation and change the layout accordingly.”
From UX’s point of view – Responsive design is a tool, not a cure-all. While using responsive design has many perks when designing across devices, using the technique does not ensure a usable experience. Teams must focus on the details of content, design, and performance in order to support users across all devices.
Source- NNG, Techabout, Medium