Large Deviations is a mathematical theory that studies the probabilities of rare events that deviate significantly from the expected outcome. It provides tools to understand how likely it is for a random variable to take on values far from its average, which is crucial in fields like statistics, finance, and engineering. The central idea is that while most outcomes cluster around the mean, large deviations occur infrequently but can have substantial impacts. This theory helps quantify the risks associated with these rare events, allowing for better decision-making in uncertain environments, such as insurance and risk management.