Surreal numbers are a unique number system that extends the concept of real numbers. They include all real numbers, as well as infinite and infinitesimal values. Surreal numbers are constructed using a recursive process that involves defining numbers in terms of sets of previously defined numbers, allowing for a rich structure that encompasses both positive and negative infinities. The creation of surreal numbers was introduced by mathematician John Horton Conway in the 1970s. This system is particularly useful in various fields of mathematics, including game theory and calculus, as it provides a way to handle quantities that are larger than any real number or smaller than any positive real number.