Responsive design is a design approach in which a website or application is developed to provide optimal viewing and user experience across a range of devices, including desktop computers, laptops, tablets and mobile phones. Responsive design ensures that the content and layout of a website or application is automatically adjusted to fit the screen size and resolution of the device. This is achieved through the use of flexible layouts, images and media queries, which allow designers to create a single design that can adapt to different screen sizes and orientations. Responsive design is important because it improves accessibility and usability. Responsive design also reduces the need for multiple versions of a website or application, simplifying the development and maintenance process.