Most typically this term is used to describe website layout design which augments itself appropriately depending on the user, specifically the browser/device they are using at the time (or sometimes how wide the browser window is let’s say.)
Be sure to read the entire wonderful ALA article about responsive design.
This term is related to the architectural and artistic installations which in a weird way “interact” with people or other things around them using cameras or other sensors. Now in web and other software development and design, this term can widely refer to all of these sorts of visual or functional augmentation of the system depending on various data received during the time of use.
