Graham's Number is an extremely large number that arises in the field of mathematics, specifically in the study of Ramsey theory. It is so vast that it cannot be expressed using conventional notation, such as powers or even power towers. Instead, mathematicians use a special notation called Knuth's up-arrow notation to describe it. The number is named after mathematician Ronald Graham, who contributed to its development. Graham's Number is so large that the observable universe is far too small to contain a physical representation of it, making it a fascinating example of how numbers can grow beyond comprehension.