This test will check if any of the webpage's JavaScript or CSS resources is blocking the render process. When the browser encounters a render blocking resource, it stops downloading the rest of the resources until these critical files are processed. In the meantime, the entire rendering process is put on hold. Aim to reduce the impact of these render-blocking URLs by inlining critical resources, deferring non-critical resources, and removing anything unused. This can greatly improve page load times and the user experience (factors which Google uses in its ranking algorithms).