Correct me if I’m wrong (cause I’m not 100% sure about this myself)…..
Responsive is when the layout of a site changes based on the screen size. Nowadays this is almost always done by using media queries, but technically, using percentages would also fall under it, because that could make things look really different on various screen sizes (and, hence, different between large monitors and small phones).
Adaptive is when the site serves different content (or a different method of content) based on the device it’s viewed on. For example, when you access the site on a desktop computer you’d get a Flash-based something, and when accessing on an iPhone, you’d see an HTML5-based something.