Dimensions: The desired dimensions of the volume.
Adjusted World Position: The transformed world coordinates of the pixel. There are two parameters, Center and Rotation, which are used to calculate these final coordinates. Those two parameters are updated every frame in the material instance, so they are in sync with the carrier medium (particle system component, decal projector, etc).
Tile Count: The number of tiles in the volume texture.
UV1/UV2: The UVs of the two neighboring tiles in the atlas which affect the final color of the pixel.
Blend Mask: The alpha to blend between the two tiles.
Volume Mask: Helps to limit the effect to the given volume. It’s necessary because the polygons carrying this material might be partially outside that volume. (Like GPU particle quads near the edge.)