Wikipedia
Megaprime
A megaprime is a prime number with at least one million decimal digits (whereas titanic prime is a prime number with at least 1,000 digits, and gigantic prime has at least 10,000 digits).
, 164 (probable) megaprimes are known, including 150 definitely primes and 14 probable primes. The first to be found was the Mersenne prime 2−1 with 2,098,960 digits, discovered in 1999 by Nayan Hajratwala, a participant in the distributed computing project GIMPS.
The term bevaprime has been proposed as a term for a prime with at least 1,000,000,000 digits.
In fact, "almost all" primes are megaprimes, as the amount of primes with more than a million digits is infinite. However, the vast majority of known primes are not megaprimes.