A great many descriptive ideas use specific terms:

Affinal: Relatives through marriage, like "husband", "wife", Mother-in-law.

Bilateral descent - Ego considers himself equally related to both his maternal and paternal sides. The terms he uses reflect that as well as his behavior. A person traces his descent or ancestry through both sides of his family. All of the kinship systems we have studied thus far are basically bilateral descent.

Clan - A group of lineages (two or more) that trace their descent back to one common mythical ancestor or ancestress. Often it's an animal, rain, thunder, etc.

Collateral relatives: Non-lineal relatives (cf. lineal relatives)

Consanguineal: Relatives through blood or common actual ancestry, like mother, father, brother, grandmother, etc.

Ego A person from whom reference is taken. (Some cultures, however, do not define kinship by ego but by reference to a kin leader.)

Extended Family: Any relative not included in one's nuclear family.

Fictive: Relatives based on legal, ceremonial or religious ties, like adopted children, godparents, etc.

Lineage - A lineage is a unilateral descent group that traces its descent back to one common ancestor or ancestress. There are two kinds: Matrilineage and Patrilineage. Cf. Unilateral descent

A person's membership in a lineage is determined by birth, and he is a member of that lineage for life.

Allegiance and responsibility are significant; commitment to a person's lineage most often comes first and may conflict with duties toward spouse, children, age-mates, etc.

Inheritance, control of property, things, even protection against enemies, are often according to lineage membership.

Marriage - Marriage to a lineage mate is very often considered incest. Marriage to someone outside of the lineage is called exogamy. Members of the same lineage are looked at by someone outside that lineage as though they were siblings... regardless of age. Note: In both cases of unilateral descent, everyone has a lineage, but the children  are in only the lineage of one of their parents, not both.

Nuclear Family: Any father, mother, and their children. There are two types:

Family of Orientation: The family in which ego learns most of his culture and in which he's oriented toward adult life. Usually his father, mother, and siblings.

Family of Procreation: The family that ego has caused by marriage and procreation. In other words, his wife and offspring.

Unilateral descent- Ego considers himself more closely related to those on either his maternal or paternal side. He is related to the other side, but not as closely. Ego traces his descent through one sex, but not the other. There are two types of unilateral descent:

Patrilineal - (or Agnatic) Is where ego traces his descent through only the males. The females are part of their father's lineage. Notice that a mother's children are not in her lineage.

Matrilineal - (or Uterine) Is where ego traces his descent through only the females. Men are not excluded from a lineage, they are members of their mother's. Yet they do not pass on their heritage to their children nor are they in the same lineage.

Note: Please do not confuse this with "lineal relatives".

Rule of Uniform Descent: If someone whom ego calls "brother" has children who ego calls "niece" or "nephew", then the children of ANY "brother" will be "niece or "nephew".

Rule of Uniform Reciprocals: If "uncle" and "nephew" are terms used between a pair of relatives, then the reciprocal of every "uncle" must be "nephew." The same would be true even with differences in sex.