A gigantic prime is a prime number with at least 10,000 decimal digits.
The term appeared in Journal of Recreational Mathematics in the article "Collecting gigantic and titanic primes" (1992) by Samuel Yates. Chris Caldwell, who continued Yates' collection in the prime pages, reports that he changed the requirement from Yates' original 5,000 digits to 10,000 digits, when he was asked to revise the article after the death of Yates. Few primes of that size were known then, but a modern personal computer can find many in a day.
The smallest gigantic prime is 109999 + 33603. It was proved prime in 2003 by Jens Franke, Thorsten Kleinjung and Tobias Wirth with their own distributed ECPP program. It was the largest ECPP proof at the time.