What the diffrent between 'twin city' and 'sister city'?

'Twin city' usually refers to two cities that are geographically close to each other; 'sister city' refers to two cities, most often in different countries, who have a co-operative, business or cultural arrangement.

there is no difference between the 2.. its just how they call it..

Various terms are used around the world to describe a long-term partnership between two communities: sister cities (United States, Mexico), twin cities (Russia, United Kingdom), friendship cities (as with relations between Japanese and Chinese cities), partnerstate (Germany), and jumelage (France) all denote the same concept of partnered communities.

Although “sister cities” is the commonly used term in the United States, some U.S. cities have formed “friendship city” relationships with communities abroad. Often, there is no difference between these terms. For example, a “friendship city” relationship might be more active than a “sister city” relationship. If there is a difference in meaning, it is that “friendship city,” in the United States tends to refer to a partnership that is slightly limited in scope.

Our European friends call us their "Twin City" while we refer to them as our "Sister City." Like other sister city programs, ours is a formal educational, economic, social and cultural partnership under Sister Cities International, which was part of President Dwight D. Eisenhower's citizen diplomacy initiative in the 1950s. Another component of the initiative is the People-to-People ambassadorship program which sends groups, primarily students, abroad on intensive multi-week educational and cultural exchanges. No matter what partner cities (as the Germans call it) call their relationship, "twinning" is generally the informal description. And, as another answerer noted, "twin cities" also refers to metropolitan areas such as Minneapolis/St. Paul that share one area but are two distinct geopolitical entities.

Nothing. They're typically called as twinned in Europe and sisters in the U.S

Another poster mentions "twin cities" such as Minneapolis and St Paul which are adjacent to each other, but that doesn't sound like what you're asking.