ISO 14644 is an international standard that outlines the classification of air cleanliness in controlled environments, such as cleanrooms. It provides guidelines for measuring and monitoring airborne particulate contamination, ensuring that environments meet specific cleanliness levels for various industries, including pharmaceuticals and electronics. The standard is divided into several parts, each addressing different aspects of cleanroom operations. It defines cleanliness classes based on the number and size of particles allowed in the air, helping organizations maintain compliance and ensure product quality in sensitive manufacturing processes.