(*plural* lexicographic orders)

- (mathematics) Formally, given two partially ordered sets A and B, the order ≤ on the Cartesian product A × B such that (a,b) ≤ (a′,b′) if and only if a < a′ or (a = a′ and b ≤ b′).
- (mathematics) Given sets (A
_{1}, A_{2}..., A_{n}) and their total orderings (<_{1}, <_{2}..., <_{n}), the order <^{d}of A_{1}× A_{2}× ... × A_{n}such that (a_{1}, a_{2}..., a_{n}) <^{d}(b_{1},b_{2}..., b_{n}) iff (∃m > 0) (∀ i < m) (a_{i}= b_{i}) and (a_{m}<_{m}b_{m})

More generally, one can define the lexicographic order (a) on the Cartesian product of n ordered sets, (b) on the Cartesian product of a countably infinite family of ordered sets, and (c) on the union of such sets.