“A subfamily is a married couple with or without children, or a single parent with one or more own never-married children under 18 years old. A subfamily does not maintain their own household, but lives in the home of someone else.
Related subfamily: A related subfamily is a married couple with or without children, or one parent with one or more own never married children under 18 years old, living in a household and related to, but not including, the person or couple who maintains the household. One example of a related subfamily is a young married couple sharing the home of the husband’s or wife’s parents. The number of related subfamilies is not included in the count of families.
Unrelated subfamily: An unrelated subfamily (formerly called a secondary family) is a married couple with or without children, or a single parent with one or more own never-married children under 18 years old living in a household. Unrelated subfamily members are not related to the householder. An unrelated subfamily may include people such as guests, partners, roommates, or resident employees and their spouses and/or children. The number of unrelated subfamily members is included in the total number of household members, but is not included in the count of family members.
Beginning in 1989, any person(s) who is not related to the householder and who is not the husband, wife, parent, or child in an unrelated subfamily is counted as an unrelated individual” (U.S. Census Bureau, 2004).