What does it mean?
'Sister Cities' is a concept of establishing a relationship between two cities that wish to create a partnership. The idea is to forge cultural and commercial ties, independent of how far from one another they might be located and are usually based on similarities between them. Most relationships occur after a meeting of two city representatives or individuals that request that their representatives initiate talks.
The first recorded case of cities creating such partnerships was recorded back in 1920 and the term Sister Cities is also sometimes replaced by Twin Cities, Twin Towns or even Friendship Cities.