prime implicant

Short definition from Wiktionary

Noun

1. 1
   A group of related 1's (implicant) on a Karnaugh map which is not subsumed by any other implicant in the same map. Equivalently (in terms of Boolean algebra), a product term which is a "minimal" implicant in the sense that removing any of its literals will yield a product term which is not an implicant (but beware: on a Karnaugh map it would appear "maximal").
2. 2
   A group of related 0's (implicant) on a Karnaugh map which is not subsumed by any other implicant (of 0's) in the same map.