Responsive design is a design approach that ensures that a website or app looks and functions well on various devices and screen sizes. With the increasing number of devices and screen sizes people use to access the internet, websites and apps must adapt to different environments. Responsive design involves creating a single, flexible design that can adapt to different screen sizes and resolutions rather than creating separate designs for each device. This helps to ensure that users have a consistent and enjoyable experience, no matter how they access the product.