Criticality safety is a specialized field within nuclear engineering and physics dedicated to the prevention of accidental uncontrolled nuclear chain reactions in systems containing fissile materials. This academic concept and applied discipline investigates the conditions under which neutron multiplication can occur and exceed safe limits, analyzing parameters such as mass, geometry, concentration, moderation, reflection, and neutron absorption to ensure subcriticality is maintained during handling, processing, storage, and transport. Its significance is fundamental to nuclear safety, mitigating the potential for criticality accidents that could release hazardous radiation.