Responsive design in general refers to the practice of making a web page that responds to a browser's viewport and other settings. Usually this is the size of the screen people are using, but it can also include their preference for a dark mode, or the fact that they use a touch device and not a mouse (in which case larger buttons are easier to hit). With responsive design, the goal is to make the website look good and work well regardless of the device people are using to access the site.
The responsive design glossary explains the many terms used in responsive design and development. It's a practical reference for anyone getting started with responsive design and development.Get an overview of all responsive design terms