A poset, or partially ordered set, is a mathematical structure that consists of a set of elements along with a binary relation that describes how these elements are ordered. In a poset, not all pairs of elements need to be comparable; that is, for some elements, neither can be said to be less than or greater than the other. The relation must be reflexive, antisymmetric, and transitive. Posets are often represented using Hasse diagrams, which visually depict the ordering of elements. They are used in various fields, including computer science, mathematics, and logic, to model hierarchical structures and relationships, such as task scheduling and data organization.