A backgammon prime (six consecutive occupied points) with one point missing.
This term is an esoteric pun derived from a mathematical method that, rather
than determining precisely whether a number is prime (has no divisors), uses a
statistical technique to decide whether the number is "probably" prime. A number
that passes this test is called a pseudoprime. The hacker backgammon usage stems
from the idea that a pseudoprime is almost as good as a prime: it does the job
of a prime until proven otherwise, and that probably won't happen.
PSDN « pseudo « Pseudocode « pseudoprime »
pseudo-random number » PseudoScheme » pseudosuit