Socialist Revolutionary Party

The Socialist Revolutionary Party (SR; Russian: Па́ртия социали́стов-революционе́ров, romanized: Pártiya sotsialístov-revolyutsionérov, lit. 'Party of Socialists-Revolutionaries') was a major socialist political party in the late Russian Empire, during both phases of the Russian Revolution, and in early Soviet Russia. The party members were known as SRs, or Esers (эсеры, esery, from the Cyrillic letters that make up the organization's acronym in Russian – С pronounced "es" and Р pronounced "er").

Source: Wikipedia — Socialist Revolutionary Party (CC BY-SA 4.0)