Fur

Houdini fur is made of hundreds or millions of curves generated on a surface. The Fur surface node generates the fur curves as scene geometry. The Fur Procedural shader generates the fur at render time instead of in the scene. You will usually use the fur surface node for visualization (with lower density) and only render fur with the fur procedural shader. In some rare circumstances you might want to generate fur geometry in the scene and manipulate it, but doing so is much slower and resource-intensive than doing it at render time.