What term describes the situation where couples live together without being legally married?

The term that describes the situation where couples live together without being legally married is cohabitation. Cohabitation refers to two individuals living together in a romantic or sexual relationship without a formal marriage ceremony. This arrangement may have legal implications in certain jurisdictions, such as rights concerning property division, child custody, and spousal support, especially after the couple has lived together for a significant period.

While common law marriage might seem relevant, it specifically refers to a legal recognition of a relationship similar to marriage based on the couple's cohabitation and their intentions to be married, which varies by jurisdiction. Additionally, separation usually implies that a married couple has decided to live apart, and pursuing marriage represents the intention to marry rather than the current living situation. Therefore, cohabitation is the most accurate term for couples living together without a legal marriage.