Variable rate shading
Lets the GPU shade a whole block of pixels with a single fragment-shader invocation wherever full resolution would not be noticed anyway.
The fragment shader is often the most expensive part of a frame, and most of that cost goes to pixels nobody is looking at closely: the edge of the screen, surfaces buried under motion blur, flat single-colour walls. VRS lets the program say "shade this region in 2×2 or 4×4 blocks" so one invocation covers several pixels. The image is still rasterized at full resolution, so edges and depth are untouched — only the shading density drops.
The feature arrived with NVIDIA's Turing (2018) and lives in Direct3D 12 and Vulkan. Tier 1 sets the rate per draw call, Tier 2 per primitive or via a screen-space image — the latter is what makes foveated rendering in VR practical.