Next of kin is a term with many interpretations depending on the jurisdiction being referred to. In some jurisdictions, such as the United States, it is used to describe a person's closest living blood relative or relatives

Kinship

Kinship is a relationship between any entities that share a genealogical origin, through either biological, cultural, or historical descent. And descent groups, lineages, etc. are treated in their own subsections....

. In others, next of kin may have no legal definition and may not necessarily refer to blood relatives at all, as in the United Kingdom.

In some legal systems, rights regarding inheritance

Inheritance

Inheritance is the practice of passing on property, titles, debts, rights and obligations upon the death of an individual. It has long played an important role in human societies...

 serve a decision making capacity (for example, in a medical emergency) where no clear will or instructions have been given, and the person has no spouse, flow to their closest relative (regardless of the age with a representative appointed if a minor), usually a child, a parent or a sibling

Sibling

Siblings are people who share at least one parent. A male sibling is called a brother; and a female sibling is called a sister. In most societies throughout the world, siblings usually grow up together and spend a good deal of their childhood socializing with one another...

.