x1 (set) and x2 (set) are sets which have non-empty mutual intersection and mutual relative complements (set subtraction; both orders of operands/directions considered); id est: x1 and x2 share at least one element, but also have a mutual symmetric difference such that neither is a subset of the other.
In other words, each of these following three sets is nonempty: x1 \setminus x, and x2 \setminus x, and the intersection of x1 with x2. There is no word/terminology in English for this concept, to krtisfranks' knowledge. x1 and x2 are mutually symmetric terbri under transposition with one another. The empty set and a universal set are disallowed for x1 (thus also x2). If x1 = x2, then x1 na klesrverlapi x2 (emphasis on "na"). This word encompasses the sets which are shown as circles in the traditional Venn diagram.