What I am describing is the genetic definition. If we are talking degrees of consanguinity it gets more complicated.
CONSANGUINITY. The relation subsisting among all the different persons descending from the same stock, or common ancestor. Vaughan, 322, 329; 2 Bl. Com. 202 Toull. Dr. Civ.. Fr. liv. 3, t. 1, ch. n 115 2 Bouv. Inst. n. 1955, et seq.
2. Some portion of the blood of the common ancestor flows through the veins of all his descendants, and though mixed with the blood flowing from many other families, yet it constitutes the kindred or alliance by blood between any two of the individuals. This relation by blood is of two kinds, lineal and collateral.
3. Lineal consanguinity is that relation which exists among persons, where one is descended from the other, as between the son and the father, or the grandfather, and so upwards in a direct ascending line; and between the father and the son, or the grandson, and so downwards in a direct descending line. Every generation in this direct course males a degree, computing either in the ascending or descending line. This being the natural mode of computing the degrees of lineal consanguinity, it has been adopted by the civil, the canon, and the common law.
4. Collateral consanguinity is the relation subsisting among persons who descend from the same common ancestor, but not from each other. It is essential to constitute this relation, that they spring from the same common root or stock, but in different branches. The mode of computing the degrees is to discover the common ancestor, to begin with him to reckon downwards, and the degree the two persons, or the more remote of them, is distant from the ancestor, is the degree of kindred subsisting between them. For instance, two brothers are related to each other in the first degree, because from the father to each of them is one degree. An uncle and a nephew are related to each other in the second degree, because the nephew is two degrees distant from the common ancestor, and the rule of computation is extended to the remotest degrees of collateral relationship. This is the mode of computation by the common and canon law. The method of computing by the civil law, is to begin at either of the persons in question and count up to the common ancestor, and then downwards to the other person, calling it a degree for each person, both ascending and descending, and the degrees they stand from each other is the degree in which they stand related. Thus, from a nephew to his father, is one degree; to the grandfather, two degrees and then to the uncle, three; which points out the relationship.