Adaptive web design
Adaptive Web Design is another term for progressive enhancement of a web site.
Adaptive Web Design also encompasses a range of other strategies which can be combined with responsive web design.
The term was first coined by Aaron Gustafson in his book "Adaptive Web Design: Crafting Rich Experiences with Progressive Enhancement" in May 2011. It is a high level design philosophy that can be achieved through a variety of execution tactics including server side user agent detection, or client side responsive web design.