– These settings control how the POINTS OF EMISSION of the particles are distributed throughout the emission locations.

– Three different types of distribution for your particle system: Jittered, Random and Grig.

Jittered: Particles are placed at jittered intervals on the emitter elements (you can notice some regularity in the distribution of emission points):

Random: Particles are emitted from random locations in the emitter’s elements.

– When applied to Faces particles born randomly on all faces.

– When applied to volume particles born randomly in the entire volume (so some particles may born on its faces).

Grid: Particles are set in a 3D grid and particles near/in the elements are kept:

– In this video you can see a Grid Distribution for a single face and for a two faces mesh.

– In the next video you can see a Grid Distribution for Volume. Note how some particles lie out of the mesh. I think this should will be fixed…

Blender Particles Source Distribution