Raster Operations Pipeline (render output unit) is a hardware
component in modern graphics processing units (GPUs) and one
of the final steps in the rendering process of modern graphics cards.
ROPs perform the transactions between the relevant buffers in
the local memory – this includes writing or reading values, as
well as blending them together.
Dedicated antialiasing hardware used to perform hardware-based
antialiasing methods like MSAA is contained in ROPs.
For those of us not in the relevant loop:
ref: https://en.wikipedia.org/wiki/Render_output_unit