Half relationships exist between individuals who have a common ancestor but descend from different spouses of that ancestor. For example, half cousins have only one grandparent in common rather than two. The term is more frequently used for siblings who have only one parent in common, for example, half brothers who have the same father but different mothers.

All the relationships discussed here (both lineal relationships and collateral relationships) are consanguineous relationships. Consanguinity is a blood relationship that exists among individuals who descend from common ancestors.

Step relationships and in-law relationships occur because  of marriage; they are not consanguineous, or blood, relationships. Examples: A stepson is the son of one’s spouse. A brother-in-law is either the husband of one’s sister or the brother of one’s spouse.