I'm really not sure, but I thought this was also referred to as same room sex or light swinging. No matter what the name, the concept does sound very interesting. I'm certain that perhaps wondering what it would be like to see my wife with another man is one thing, and actually witnessing it is something else.
The same room thing though raises a great many thoughts. Some time ago my wife and I shared a motel room with some good friends and we went back to the room before our friends who opted to continuing partying. By the time our friends returned to the room we were quite involved in some under the blanket foreplay. Once we believed our friends were asleep, we quietly finished. It was kind of hot thinking that we did this in the same room as our friends without them knowing. Once my wife thought that our friends knew (which they didn't) she confessed. Now it is kind of hot knowing that they know.
Alas our day where we may have the opportunity to do this MGS are likely gone. If you and your wife are both interested and able I hope you go for it. Life seems too short.
BTW, a google for "Monogamous group sex" returns this thread at number 3.
