can anyone explain in the simplest terms please what is the difference between a point cloud and a voxel mesh?
A point cloud is often derived by sampling. Each point represents an observation. Sometimes, a point cloud is turned into a surface by fitting triangles to the points in the form of an STL file.
A raster is a 2D grid of pixels. It divides the area of an image into constant-sized little squares. Each of these squares has a value.
A 3D raster is made of voxels. It divides 3-space into constant-sized little cubes. Each of these cubes has a value.
Pixels and voxels are rendering techniques. A point cloud is a sampling technique.
The Wikipedia article, https://en.wikipedia.org/wiki/Voxel, is helpful.
In a real system the pixels may not be square or the voxels not strictly cubic, but in every system I've worked with, they do form a regular tiling of the plane for pixels, and fill 3d space for voxels.