Adaptive and responsive can be viewed as separate dimensions of an app: you can have an adaptive app that is not responsive, or vice versa. And, of course, an app can be both, or neither.

Responsive

Typically, a responsive app has had its layout tuned for the available screen size. Often this means (for example), re-laying out the UI if the user resizes the window, or changes the device’s orientation. This is especially necessary when the same app can run on a variety of devices, from a watch, phone, tablet, to a laptop or desktop computer.

Adaptive

Adapting an app to run on different device types, such as mobile and desktop, requires dealing with mouse and keyboard input, as well as touch input. It also means there are different expectations about the app’s visual density, how component selection works (cascading menus vs bottom sheets, for example), using platform-specific features (such as top-level windows), and more.