Sisterhood is like two petals of a flower and refers to beautiful-looking biological sisters. Such sisters might get together to watch TV, go to the movies, talk, gossip, drink, dance, and so on.
Later it became a kind of network language, refers to the relationship is particularly good bosom friend, general refers to the love of the sister of good friends. Sister is a kind of kinship, if it is a direct blood relative, it refers to two people who have the same parents, if it is a collateral blood relative, usually refers to the cousin relationship.