Secondary, secondary partner, or secondary relationship is a term used in polyamorous relationships to refer to a partner who is not one's primary partner. This works differently for different people. For some, the term is descriptive, meaning they apply it to a relationship that is simply more casual with less involvement than their primary relationship. For others, it is prescriptive; they use it to define what relationships outside their primary partnership are allowed to be.
More About Secondary
The term secondary can be a bit fraught for some as, depending on who you are dealing with, it can lead to a sort of "second class citizen" status in a poly relationship. This is where the questions of descriptive versus prescriptive becomes important. Prescriptive secondary relationships will demand that a secondary partner always recognize their role as "less than" the primary relationship.
