Invert Grid

– Imagine your mesh inside a box filled with small spheres (the particles). The number of cubes along the longest side is given by Resolution.

– Invert Grid Unchecked: If a particle of the grid fits inside the mesh then it’s visualized.

– Invert Grid Checked: If a particle of the grid fits outside the mesh then it’s visualized.

– In this example you can see how Invert Grid works for Volumes:

Blender Partice Grid Invert