So it certainly goes beyond formally Married couples.The FAMily record is used to record marriages, common law marriages, and family unions caused by two people becoming the parents of a child. There can be no more than one HUSB/father and one WIFE/mother listed in each FAM_RECORD. If, for example, a man participated in more than one family union, then he would appear in more than one FAM_RECORD. The family record structure assumes that the HUSB/father is male and WIFE/mother is female.
The preferred order of the CHILdren pointers within a FAMily structure is chronological by birth.
Some definitions for 'family' say it is a group of individuals who share a legal or genetic bond.
So, even a 'one-nighter' resulting in child would share at least a genetic bond and thus classed as a 'loose' family.
To build a biological/genetic 'family' tree, the parents and the child are a type of family.