In the theory of functions of several complex variables, a branch of mathematics, a polydisc is a Cartesian product of discs. More specifically, if we denote by the open disc of center z and radius r in the complex plane, then an open polydisc is a set of the form It can be equivalently written as One should not confuse the polydisc with the open ball in Cn, which is defined as Here, the norm is the Euclidean distance in Cn. When the term bidisc is sometimes used. A polydisc is an example of logarithmically convex Reinhardt domain.