Point clouds are procedurally created groups of particles that can be assigned as point sources in the same way any particle simulation can be. They are differentiated from particle simulations in that any animation assigned or applied is either pre-generated, as is the case with the RealFlow particle importer, or kinematic in nature (meaning it is assigned with keyframes, not through an evaluated simulation).
The particle generator allows you to easily create ordered arrays of particles, while the point cloud generates a volume of random particles. The surface particle generator is used to create randomly placed particles over a geometric surface. Once created, you can assign these items as point sources for Replicators, Blobs, Sprites or Volumes.