Well the sweet and short definition I have is they look somewhat like peonies, Tons of petals. Puts me in the mind of an English rose. Or my interpretation of an english rose. There are some roses such as latin ambiance that I'm not so sure if they fall into the category of garden roses,but they sure look like it to me when they open.
And some of the varieties are really expensive.
Somebody had posted on FC a while back about some grower having a garden rose design contest. Maybe that person will speak up........
Oh and If I'm wrong in my definition, I for sure know someone will correct me