Class S(クラスSKurasu Esu), or "S kankei", abbreviated either as S or Esu(エス), is an early twentieth century Japanese wasei-eigo term specifically used to refer to strong emotional bonds between schoolgirls, and a genre of girl's fiction(少女小説shōjo shōsetsu) which tells stories about the same, particularly a mutual crush between an upperclassman and an underclassman. The S is an abbreviation that can stand for "sister", "shōjo"(少女, lit. young girl), "sex", "schöne", and "escape".