Good question. We all know that Google took its name from a mispelling of the word Googol but what exactly is one when it's at home? This article explains it pretty well, with some great comparisons too which help us get our heads around such an enormous number.
From the article:
How many grains of sand are there on the beach at Coney Island in New York City? How many raindrops fall on London in a year? What is the number of words that have been spoken in all the history of mankind? How many electrons are there in a thimbleful of air?