The design of web pages that provides their correct display on different devices and adapts to the specified size of the browser window. Main goal of Adaptive design is to make the product available on all devices and screens of specific size, providing the best possible experience for all users.
In early 2010, mobile browsers (what to adapt) and media expressions (how to adapt) appeared. At this time, books were published that gave names to the approaches: “Adaptive Web Design” by Aaron Gustafson and “Responsive Web Design” by Ethan Marcotte.
To be clear about the difference we wrote this Q&A: What Is the Difference Between Responsive and Adaptive Design?