SOB' is an acronym for 'Sister of Blood'%2C which is a term used in the African-American community to describe a close friend or family member. The term was coined by the poet Langston Hughes in his 1926 poem 'The Negro Speaks of Rivers'. It is used to describe a deep bond between two people that goes beyond the typical relationship of siblings. The term can also be used to describe a story that has a strong emotional connection to the reader.