"Fraternal" is an adjective used to describe a brotherly relationship. The term can be used to denote male platonic relations, whether the people being described are part of the same family or not. It may also be used to refer to social groups that grant membership only to men.
The word "fraternal" originally comes from the Latin word "frater," meaning "brother." In biology, the term is used to differentiate between identical and non-identical twins. Fraternal twins are not identical, as they develop from separate eggs. Despite the primary meaning of the word, fraternal twins can consist of two females, two males or one child of each sex.