Ten to the 100th power is the number 1 followed by 100 zeros, also called a "googol." A googol exceeds the total number of atoms in the observable universe.
The word "googol" was first used by Milton Sirotta in 1938. The googol itself has no real mathematical significance other than to demonstrate the magnitude of numbers. The googol has two prime factors, the numbers two and five, and there are 100 of each of those numbers in the prime factorization. To get an idea of how large a googol is, remember that 10^6 is one million and 10^9 is one billion.