Trent Walton on the term Device-Agnostic:
Like cars designed to perform in extreme heat or on icy roads, websites should be built to face the reality of the web’s inherent variability. In my mind this approach addresses the following from the beginning: Hostile browsers, Tiny screens, Slow connection speeds, and Touch inputs
Long story short, as heard before: we’re undoing the wrong stuff we did the past few years (fixed width designs and the like). RWD and being Device-Agnostic are just Web Design Done Right™
I use the term device-agnostic, now synonymous (to me) with good web design, to distinguish sites that embrace the inherent variability of the web—which, in itself, is nothing new.