1. a cardinal number represented as 1 followed by a googol of zeros (ten raised to the power of a googol);

WordNet (r) 3.0 (2006):

googolplex n 1: a cardinal number represented as 1 followed by a googol of zeros (ten raised to the power of a googol)The Free On-line Dictionary of Computing (30 December 2018):

googolplexThe number represented in base-ten by a one with a googol zeroes after it. (2001-03-29)