Sorry to be a smart-ass
I 2nd the anti-labels sentiment...
Labels can be useful as quick references, but I hesitate to use them as anything more than that.
The risk is that people get wrapped up in trying to force their relationships to fit into labels they've already chosen, rather than letting relationships develop in their own right.
For example, Hetero Couple A meets Hetero Couple B. There's the right chemistry, and they start dating. They call themselves a quad. Eventually, the romance between Woman A and Man B dies out, but their partners are still wildly in love. Now, did the quad define the relationship, or did the relationship at the time define the quad? Do Man A and Woman B have to break-up because the quad didn't work out? Or do they accept that the relationship dynamic has changed, and drop the label?