Interesting topic :-), I would say that it is one where two people commit to each other and help and assist each others growth. Of course there has to be an understanding from both parties for this to be achieved otherwise it's going to be a waste of energy for one of them. They should give the time to connect with each other emotionally, mentally, physically, and spiritual in order to gain a full understanding and obtain a united bond where giving is done and there is no need to take as the energies only need to be received.

That's my perspective anyway :-)