The German Society for Musical Performing and Mechanical Reproduction Rights (GEMA) is a state authorized collecting society and performance rights organization baed in Germany, with administrative offices based in Berlin and Munich. GEMA represents the usage rights stemming from authors' rights for the musical works of those composers, lyricists, and publishers who are members in the organization. It is the only such institution in Germany and a member of BIEM and CISAC. The entire GEMA organization is grounded in one simple idea: whoever uses music publicly should pay the authors for the use of their music.
Music Publishing is the business of protecting and promoting song copyrights and collecting the royalties that these copyrights generate. Think of a song as intellectual property (it's an original piece of art!), and music publishing as the business that makes sure that songwriters get paid a fair compensation when their intellectual property is used by companies. Those companies could be record labels (mechanical royalties), radio stations, bars, and restaurants (performance royalties), or film studios and advertising agencies (sync license fees), and many more.