SisterSite is an invention of WardsWiki. See SisterSites.
Now we propose a user-defined concept, named PartnerWiki as a CommunitySolution, that could be supported by a TechnologySolution (with realtime creation of PartnerPages and PartnerWikis)
The pseudo-icons <=>, <-> at the bottom of the page stand as examples for a proposed notion to make user-defined "Sister Sites", which we could call PartnerWikis, if you prefer this notion.
PartnerPages are bidirectionally connected pages, where their respective links are listed at the bottom of the involved pages.
PartnerWikis are Wikis connected by PartnerPages, which in the weak form have "<->" connections and in the strong form have '<=>' connections.
In the strong form "<=>", the coupled pages are bidirectionally linked namesakes as used in the classical SisterSite concept.
In the weak form '<->', the coupled pages are "only" visibly bidirectionally linked pages.
<=> http://www.usemod.com/cgi-bin/mb.pl?SisterSite,.. This is an example of a user-defined Namesake Partner Page Link list
<-> SisterSites,.. This is an example of a user-defined Partner Page Link list