Original: Friedrichshain-Kreuzberg is the second borough of Berlin, formed in 2001 by merging the former East Berlin borough of Friedrichshain and the former West Berlin borough of Kreuzberg.
Simplified: Friedrichshain-Kreuzberg is a borough of Berlin. It is a new borough, only made in 2001 by joining the old boroughs of Friedrichshain and Kreuzberg.