No! Definitely not.
Two is such a limiting number.
All that has been said before... if you started to categorize and number them, would far exceed such a lonely number... (I hear a song-worm growing in my head.)
sidhewolf has a great handle on this topic (as do others.)
I think the most interesting thing is how "poly" has morphed (a lot like bdsm has) since the internet has come along. Open (and semi-open) marriages were about all that was "available" to new couples 15-20-30+ years ago... and those of us who chose that, had to deal with it without all the information available to you today.