Wow I have learned a lot on this thread. Probably most important is gamblergords information that I never rode any of my late eightys to mid ninetys mountain bikes on trails. Wonder how old that guy is.
Was not going to join this thread, but here is my definition. One kind of road bike is anything ridden by someone who, after you have kept up with a group on a thirty mile ride you rode 15 miles to get to, and will be riding home from, tells you that you should probably either think about getting a real bike or giving up the sport. They then put it on the rack of their car and drive it four miles home.
The bike I was on was a mid eightys Fuji s-10s, converted to SA three speed hub with 27x1" tires, fenders, and non areo levers.
Luckily that guy found a new hobby and no longer rides. I believe that what stopped him was driving into a low hanging fast food drive through with the bike on the roof...