It could involve a spectrum of activities such as * Occasionally kisses other people * OK with oneself and SO dancing with other people with physical contact

It could involve a spectrum of activities such as * Occasionally kisses other people * OK with oneself and SO dancing with other people with physical contact * One of the members of the partnership does some form of sex work (including phone-sex operator, webcam peformer, exotic dancer, etc) * Occasional threesomes None of these would be monogamous by some definition, but some would consider these different from a style of nommonogamy where someone dates entirely separately from their partner(s)