The theory of lattices in the sense of order theory. For the number-theoretic notion, use the tag "lattices" instead.

This tag is for lattices in the sense of order theory. For the number-theoretic notion, use the tag instead. A lattice is a poset where any two elements $a$, $b$ have a least upper bound $a\vee b$ and a greatest lower bound $a\wedge b$. Some important classes of lattices are complete lattices, distributive lattices, and modular lattices.