x1 (set/family/tree graph) is a crown category/clade/'group'/set formed from and defined by (elements of) set x2 (nonempty set/family/graph), which have set-wide simultaneous most-recent common ancestor(s) x3, according to judge/standard/definition/(directed) tree graph/relations x4.
A crown clade is the set of all descendants, living or dead, of some 'individual(s)' x3 = A which is/are the most recent common ancestor(s) of all of the elements in x2 (provided that such an ancestor be well-defined and exists), united with the minimal set which contains A (taken as individual entities, not as a collective set thereof); in other words, it is A and all of the descendants thereof which have ever existed. The elements of x2 need not necessarily be presently alive (or dead, for that matter), so long as they conceptually exist and are well-defined and allow such a common ancestor to exist; this means that this definition is somewhat more general than the common usage of "crown clade" in English. Ancestor(s) A is/are essentially unique (modulo gender/parenting roles and polygamy), although they often may be conceptually extended to include an entire taxon to which the true A belong(s). x4 allows for relations and (directed) tree graphs other than those of/by biological parentage/inheritance. See also: "kloje", "tseingu", "kleide", "klesi".