Adaptive design refers to the practice of creating different sites that are adapted to a specific platform. The most well-known examples are mobile sites that are usually located at m.example.com. With adaptive design, you reduce the complexity of each site, but you are left maintaining multiple sites. Users visiting one of the site rather than the other could also be left with a bad experience.
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