I see Blender 2.76 now has a feature called "Point Density" textures. Is this a particle system? If so, how is it different from previous particle systems?
3$\begingroup$ related: blender.stackexchange.com/questions/45481/… $\endgroup$– user1853Feb 11, 2016 at 14:58
Point Density Textures are a way of rendering particles or mesh vertices as volumetric halos in Cycles.
A halo is basically a little volumetric ball. You can accomplish essentially the same effect without point clouds by using dupliverts or a particle system with little spheres as particles. However point density textures are much more efficient due to requiring a much simpler BVH, since the entire volume is within one object, instead of hundreds of thousands of little overlapping objects.
The above example uses a particle system with 250,000 particles and a turbulence force field. To render it as a point cloud I created a "domain" object (a scaled cube) around the particle system and gave it a volumetric emission shader using the Density from the Point Density as the emission strength. See this answer for how to set up a point density texture.
Basically, it is a way of using particles or a mesh's vertices to drive the density of a volumetric material. You will need to use a Point Density texture and set the emitter object/mesh.