Absolute zero is the theoretical temperature at which the constituent particles of a physical substance possess the minimum possible random kinetic energy. It is quantified as 0 Kelvin and represents the absolute lowest limit of temperature within the thermodynamic scale. At this point, the thermal energy and motion of atoms and molecules approach a theoretical standstill. The concept is fundamental to thermodynamics, as it defines the state where further cooling is impossible and where systems theoretically achieve their lowest internal energy state. While the concept of zero entropy is key to understanding this state, attaining and maintaining absolute zero remains an extreme technological challenge due to unavoidable interactions with external energy fields.