gtownviking

I am a newbie still. Only been in the road bike "scene"(sort of) for about three years.
I have come to realize that I like "bumming" around my neighborhood in the evenings and using my bike to go get groceries. I also like charity rides and touring. You will not find me participating in a crit anytime soon.

so now that you know me a little....

Somebody explain to me the difference between a Randonnuer and a Fully Loaded touring bike? And don't say one is loaded at all four corners., I'm talking geometry, components, etc...and is there really a need for the two different bikes?
Also...
What is a Brevet?
What constitutes a bike as being a "Sport" bike?
Same for a "Sport Tourer"?
Are drop bars the only requisite for a bike being called a "road" bike?

If I could only have three "road" bikes in my stable, what would you tell me to get and why?
Conditions are. I like to tour, bum around the neighborhood in the evenings and get groceries at the corner store, and charity/event rides.

I guess what I am getting at is this. Is there an "etiquette" to what bike to ride for certain event? Other than the obvious. You don't show up with an LHT to your Tuesday Night Crit.

Thanks for sharing your wisdom.