From The Art and Popular Culture Encyclopedia
Polyamory (from poly=multiple + amor=love) is the desire, practice, or acceptance of having more than one loving, intimate relationship at a time with the full knowledge and consent of everyone involved. Polyamorous perspectives differ from monogamous perspectives, in that they respect a partner's wish to have second or further meaningful relationships and to accommodate these alongside their existing relationships.
The term polyamory is sometimes abbreviated to poly, especially as a form of self-description, and is sometimes described as consensual and/or responsible non-monogamy. Polyamory is usually taken as a description of a lifestyle or relational choice and philosophy, rather than of individuals' actual relationship status at a given moment. There is a certain fluidity in its definition, to accommodate the different shades of meaning which might be covered. Polyamorous relationships are themselves varied, reflecting the choices and philosophies of the individuals concerned.
Polyamory is distinct from polygamy, being closer to a personal outlook than a predefined bonding system. It is grounded in such concepts as choice, trust, equality of freewill, and the more novel idea of compersion, rather than in cultural or religious tradition.