The largest named number in the world is a googolplexian. Because numbers are infinite, and any number can be made larger by simply adding to it, the largest number in the world is defined as the largest number that has a name.
A googolplexian is described as a “1” with a googolplex of zeroes following it. A googolplex is described as a “1” with a googol zeroes behind it. A googol is equal to a “1” with 100 zeroes following it. Most of these numbers are too large to have any value in equations, and they are rarely, if ever, used by mathematicians.