Probability theory is the branch of mathematics concerned with analyzing random phenomena. It studies random variables, stochastic processes, and events that occur randomly or with uncertainty. While individual events are unpredictable, repeating events will exhibit statistical patterns that can be studied and predicted using tools from probability theory like the law of large numbers and central limit theorem. The mathematical foundations of modern probability theory were established by Kolmogorov. Probability theory has applications in fields like risk assessment, decision-making, reliability analysis, and more.