Or micro-subdivision or tesselation or whatever you want to call it. Normally, I'll trust Andrew Price's tutorials to get into the detail. Since Micro-polygon displacement came to Blender, I've found it almost unusable because of the memory issues. However, Greb Alexander is also on my youtube feeds, and browsing around his channel tonight, I came across https://www.youtube.com/watch?v=hlh9rrjG29k. This is just part one, and a much more in depth look at the new feature, including ways to beat the, in particular, VRAM limitations. I experimented with a scene that could really benefit from the feature, but simply wouldn't render on GPU because of the VRAM problems using his optimisation techniques, and I have hopes for getting there now. A much more detailed look at the feature, and well worth a watch. I have yet to watch part 2, but hoping that it's as informative.