Dual or Duals may refer to: Paired/two things. Dual (mathematics), a notion of paired concepts that mirror one another. Dual (category theory), a formalization of mathematical duality. see more cases in Category:Duality theories. Dual number, a number system used in automatic differentiation. Dual (grammatical number), a grammatical category used in some languages. Dual county, a Gaelic games county which competes in both Gaelic football and hurling. Dual diagnosis, a psychiatric diagnosis of co-occurrence of substance abuse and a mental problem.
https://en.wikipedia.org/wiki/Dual