Polygamy can be defined as any "form of marriage in which a person [has] more than one spouse." - from wikipedia http://en.wikipedia.org/wiki/Polygamy.
In the United States the primary practitioners of polygamy are fundamentalist Mormons, and in practice means one man married to multiple women.
Polyamory (from Greek πολυ [poly, meaning many or several] and Latin amor [literally “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 reflect one or more partner's wish(es) to have further meaningful relationships and to accommodate these alongside their existing relationships. - http://en.wikipedia.org/wiki/Polyamory.
In practice this can vary from several relationships of equal standing to a primary relationship and several secondary relationships to an open relationship or a group marriage. The important things in any type of polyamorous relationship is that all persons involved know that their partners are also involved with other people, that no-one is jealous, and that trust and communication are at the forefront of all the relationships.
An open relationship denotes a relationship (usually between two people) in which participants are free to take other partners; if the couple making this agreement are married, it is an open marriage. While "open relationship" is sometimes used as a synonym for "polyamory" or "polyamorous relationship", these terms are generally differentiated. The "open" in "open relationship" usually refers to the sexual aspect of a non-closed relationship, whereas "polyamory" refers to the extension of a relationship by allowing bonds to form (which may be sexual or otherwise) as additional long term relationships. http://en.wikipedia.org/wiki/Open_relationship
This means that there is an agreement between the people involved that other sexual partners are allowed, usually within some set of guidelines that both people agree on.
i've figured out that for me monogamy doesn't work - i'm bisexual for one thing, but even more than that sex /= love for me, and being able to have sex with who i want when i want is something i'm not willing to give up on again - every time i've tried monogamy i've either wound up cheating or i've sabotaged the relationship when i wanted someone else - a lot of years of serial monogamy and misery later i finally figured it out
my life with zooom started out as a one night stand and developed into an open relationship in which we could both sleep with other women with advance permission; in time this changed to an open relationship where we could sleep with whomever we wished (he had a hard time w/ the concept of me sleeping with other men) and permission in advance wasn't required although honesty was still necessary (ie: we wanted to know who/when our partners slept with other people) to a form of polyamory (in that we were both seeing other partners who we also loved, although mine was love as a friend and his was in love with...)
the relationship worked for both of us for about 12 years before it fell apart - and the breakup wasn't either of our faults; we'd both changed a lot over those years and somewhere along the way we went from in love with each other to loving one another but not in love or sexually interested anymore at which point it was time for a change
currently i'm in another open relationship (i'm still surprised by this; i wasn't sure i was ready but it works really well so far) - a bit different this time, in that we both agreed from the beginning that we weren't monogamous or going to be, that as long as honesty and safe sex were practiced permission wasn't necessary, and we could sleep with whoever we wanted - this works for both of us and i hope it continues to work for a long long time - we're good together and we still get to have fun (i can sleep with the good friend who i love dearly but i know will break my heart if i tried to have a serious relationship with and date a beautiful girl occasionally, he gets to flirt with other women and go home with them if he wants, if we meet someone who's interested we're happy with group play, and we both get to have each other which is grand)
so... what's my point? i'm not sure there's really a point to this, other than i'm over being judged based on the way i choose to live my life, and i'm really tired of people confusing polygamy with polyamory with an open relationship - i'm happy, he's happy, we both have other interests and that's all good
edit to add... this post is not directed at anyone in particular here, and most of those on my lj don't judge (or at least you don't say so) - but other people in our scene seem to have issues
quesions/comments/discussion welcome... i know a lot of you don't get this, and i can accept that... i understand that you want monogamy but i can't quite wrap my head around the judgemental attitudes we get, especially from what is supposed to be an open and accepting group (ie: freaks)