partially ordered set
Antimatroid, a formalization of orderings on a set that allows more general families of orderings than posets Causal set, a poset-based approach to quantum gravity directed set – Set with a preorder in which any two elements are always both less than or equal to some third element Lattice – Abstract structure studied in the mathematical subdisciplines of order theory and abstract algebra Poset topology, a kind of topological space that can be defined from any poset Strict weak ordering – strict partial order "<" in which the relation "neither a < b nor b < a" is transitive. Tree – Data structure of set inclusion Zorn's lemma – Mathematical proposition equivalent to the axiom of choice