What distinguishes adaptive web design from responsive web design?

Adaptive web design is characterized by its use of fixed layouts specifically tailored for a set number of screen sizes. This means that an adaptive design will serve different layout files to different devices, such as desktops, tablets, or smartphones, typically detecting the device and delivering the most appropriate layout based on its predefined breakpoints.

The essence of adaptive design lies in its ability to create a distinct user experience for various device types, ensuring that each user is presented with an optimized version of the site that fits their specific device category. This is in contrast to responsive web design, which fluidly adapts to screen sizes using flexible grids and percentages, offering a continuous, cohesive experience as the user resizes their browser or switches devices.

In the context of the other options, adaptive design does not adjust fluidly to any screen size, as this describes responsive design. Responsive design also does not require separate URLs; it operates under a single URL for all devices, adapting the layout accordingly. Lastly, responsive design makes use of CSS media queries to adjust layouts rather than relying solely on JavaScript, supporting a more graceful and lightweight solution for responsive experiences.