Critical phenomena refer to the behavior of physical systems as they approach a phase transition, such as from liquid to gas. At this point, small changes in temperature or pressure can lead to significant changes in the system's properties. This behavior is characterized by fluctuations that become larger and more correlated, leading to a state of criticality. These phenomena are often studied in the context of statistical mechanics and thermodynamics. They help scientists understand complex systems, including magnetic materials and fluid dynamics, by revealing how microscopic interactions can lead to macroscopic behaviors during transitions.