The Free On-line Dictionary of Computing (30 December 2018):

dual-stack

    A term used to describe a network node running both
   IPv4 and IPv6 protocol stacks (or possibly others) at the
   same time.  Such a machine can act as a protocol converter
   between the two networks.

   A node without dual-stack support can relay traffic in a protocol
   it does not support natively by use of tunnelling.

   RFC 4213 (http://tools.ietf.org/html/rfc4213)

   (2013-10-08)