The dream Sugar.  The perfect NSA relationship.  Think of the best girlfriend you could dream of.  She is hot, kinky, fun as hell, no maintenance, reasonable cost, spends lots of time loving on you and goes crazy in appreciation when you do special for her.   Think 9/9 or above on TER scale.

Kind of like a wife

Try searching the board for past definitions of "Unicorn".  I  posted one a while back, as have others.  

Remember the old PSA's from the past:  Reading is fundamental.

The ladies I know are referring to "hot vs. Crazy matrix"

Depends on where you are.  If you are a swinger, it's a single bi woman.  If in the vanilla world, the hot/crazy matrix defines it as a woman that is an 8 or 9 hot but less than 5 crazy.  It also advises that it doesn't exist, and that if you are dating a woman that falls in this range, that you are dating a dude.