Abbreviation of 社会民主党 (しゃかいみんしゅとう). Used in political contexts to refer to the party or its members.
See also: 社会民主党
The Social Democratic Party announced new policies for the upcoming election.
Social Democratic Party
Abbreviation formed from the first characters of 社会 (しゃかい, 'social') and 民主 (みんしゅ, 'democratic').