$~$10^{100},$~$ i.e., 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.
The search engine Google is named after the number googol. (The difference for the spelling, as the apocryphal story goes, comes from the fact that one of the early Google investors misspelled the name on a check.)