What does "de facto" refer to in terms of family structure?

In the context of family structure, "de facto" refers specifically to unmarried couples who live together in a long-term, committed relationship that resembles a marriage. This term is often used to signify a partnership that has many of the characteristics of marriage, such as sharing a household and intimate relationships, but without the legal recognition of marriage.

This understanding of "de facto" relationships helps clarify societal norms and legal frameworks surrounding different family structures, including issues related to property rights, healthcare decisions, and parental responsibilities. The other options refer to different familial or living arrangements that do not fit the definition of a "de facto" relationship, focusing instead on various types of family dynamics that either require legal marriage or do not involve a romantic relationship at all.