Basic Vocabulary ----------Note: As with most of the rest of the english launguage, precise defintions of these words vary from person to person and from group to group. Your mileage may vary.
Closed- A relationship is closed if there is an agreement among the members to not get sexually and/or romantically involved with anyone outside the relationship. A monogamous relationship is a closed two-person relationship.
Group Marriage- A marriage involving more than two people. Not legally recongnized in the U.S. or by most major religions in western society. Many people do it anyway, often making legal agreements that function similarly to the legalities in a usual marriage.
Open- A relationship is open if there is an agreement among the members that it is acceptable to get sexually and/or romantically involved outside of the relationship. Specific rules within a relationship about such involvement are usually negotiated to best fit the people in the relationship.
Partner- Short for "Life Partner." Gender-free, hetero-assumption-free term for someone with whom one is involved. Usually in a primary relationship. Also sometimes used in different contests as short for "sexual partner".
Poly- Short for polyamorous, usually used as an adjective. A poly relationship is a non-monogamous relationship. A poly reltationship is someone in, or at least interested in, a poly relationship.
Polyamory- Literally, "Many Lovers." A generic term for non-monogamy.
Polyandry- Having more then one husband.
Polyfidelity- Closed relationship involving more then two people. The members of a group marriage, for example, may limit their sexual/romantic involvement to the members of the group.
Polygamy- Having more then one spouse.
Polygyny- Having more then one wife.
Primary Relationship(s)- The relationship(s) which is (are) the most inportant and typically involve a high degree of commitment, such as the relationship with a marriage partner.