POSSLQ, an acronym for "Persons of Opposite Sex Sharing Living Quarters," was a term coined in the 1970s by the United States Census Bureau as a way to categorize unmarried couples who lived together. Since then, the term has fallen out of favor due to its clunkiness and binary language.
Nowadays, there are various synonyms that represent diverse living arrangements, such as cohabitating, domestic partners, common-law couples, and roommates. These terms are more inclusive of the LGBT+ community and non-traditional relationship dynamics. As language continues to evolve, it's important to be aware of how we talk about relationships and strive for more inclusive terminology.