Parallel Cousins vs Cross Cousins
Parallel cousins are offspring of siblings of the same sex. A parallel cousin is a first cousin who is paternal uncle's child or maternal aunt's child, while a Cross Cousin is maternal uncle's child or paternal aunt's child. Parallel cousin is a consanguinial kin who is in the same descent group as the subject and from the parent's same-sexed sibling. First cousins may either be the children of two brothers (patrilateral decent parallel cousins), of two sisters (matrilateral decent parallel cousins).
In the Seri kinship system, cross and parallel cousins are called by the same terms as those used for siblings. Parallel cousins, the children of one's father's brother or one's mother's sister, are treated as brothers and sisters. Parallel cousins are treated with the same avoidances as real brothers and sisters. Like true brothers and sisters, parallel cousins are referred to with the terms tuakaqu (an older brother or sister) and taciqu (a younger brother or sister).
In Fijian society, one's parallel cousins are considered to be brothers, the new chief is often not a true son or brother of the former one.
In Iroquois system and among Hindus marriage is promoted between cross cousins. Parallel cousins not the subject of promoted marriage since a union in many cultures would fall under an incest taboo. In a patrilineage, parallel cousins are part of the subject's unilineage whereas cross cousins are not. In matrilineal societies, parallel cousins are considered to be related to the subject while cross cousins are not.
Parallel cousins are entitled to anything belonging to another parallel cousin. Technically, parallel cousins could enter the home of a tuakaqu or taciqu and take anything that they wanted.
Although this rarely happens, parallel cousins must be willing to sacrifice anything they own for each other. As parallel cousins are treated as brothers and sisters, so too the parents of parallel cousins are referred to as mother and father.
The distinction between cross cousins and parallel cousins is often an extremely important one in traditional societies.