A more thorough explanation:

Definition: CUPOS stands for "a cohabiting unmarried person of the opposite sex." It is similar to the term POSSLQ, which stands for "a person of the opposite sex sharing living quarters," but CUPOS specifically excludes married individuals.

For example, if a man and a woman are living together but are not married, they would be considered CUPOS. However, if they were married, they would not be considered CUPOS but would still be considered POSSLQ.

These terms are often used by the Census Bureau to gather information about living arrangements and household demographics.