If you're reading this, you probably know what primes are. It's possible to get four primes in one 'decade', which is called a prime quadruplet. An example is 1481, 1483, 1487, 1489. A fifth prime may be found close to a prime quadruplet, either being the four less than the first prime, or four more than the last prime. An example is 1481, 1483, 1487, 1489, 1493. This is a prime quintuplet.
For further information, go to Wikipedia, for example.