Noun
Helly family (plural Helly families)
(combinatorics) A family of order k of sets, such that any minimal subfamily with an empty intersection has k or fewer sets in it.
For instance, the closed intervals of the real numbers form a Helly family: if a family of closed intervals has an empty intersection and is minimal (i.e. no subfamily of the family has an empty intersection), it must be pairwise disjoint. citation. Source: Internet