What is the difference between sparse and dense clouds?

Sparse point cloud is only the first stage of creating a workable model. In the sparse point cloud, as the name suggests, there are only few points in comparison to the dense point cloud, so the object itself can be hard to discern at this stage.

Dense point cloud is the second stage of processing, and it is required to start measuring and creating digital elevation maps and orthophotos down the line. Dense point cloud creation is also the lengthiest step.