A doubly-connected planar domain between two closed Jordan curves without common points, one of each encloses the other.
For an annular domain with respect to a quadratic differential, see Global structure of trajectories of a quadratic differential.
Annular domain. E.D. Solomentsev (originator), Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Annular_domain&oldid=14515