I did a search and did not find much on it. However from what I gathered, it is a dimly lit bar with semi-private tables or areas that are ideal for making out. Here is a review of bar in NY that is considered a smooch bar (??snogging?? is that what the kids are calling these days?):
"Miraculously undiscovered (so far) by the bar tourists, Bouche feels like a cool house party you've just happened to stumble into. Imagine all the ingredients of the quintessential downtown lounge—exposed-brick walls, local artwork, violet-hued lighting, shabby-chic couches—shrunk down to Mini-Me size, including the space itself; you'll walk by a few times before noticing the door. Speaking of bouche (French for "mouth"), the hidden, cushion-lined nook along the west wall is tailor-made for snogging, and the bar's so dark you could easily do more with no one the wiser."