Particle size refers to the dimensions of individual particles in a material, which can range from very small, like atoms and molecules, to larger particles, such as grains of sand. It is an important characteristic in various fields, including pharmaceuticals, materials science, and environmental science, as it can influence the behavior and properties of substances. Measuring particle size can be done using different techniques, such as sieving, laser diffraction, or dynamic light scattering. The size of particles affects how they interact with each other and their surroundings, impacting processes like dissolution, sedimentation, and reactivity. Understanding particle size is crucial for optimizing product performance and ensuring quality control.