Packing density is a term used in materials science and engineering to describe the proportion of solid material in a given volume. It refers to how efficiently particles or molecules are packed together within a given space. High packing density indicates that the particles are closely packed together, leading to higher material density and potentially improved properties such as strength, conductivity, or thermal conductivity. Research in packing density generally aims to optimize the packing of particles or molecules in various materials to achieve desired properties and performance. This research area has applications in fields such as pharmaceuticals, ceramics, and composites.