Did anyone see that movie The Girlfriend Experience
that Sasha Gray was in?
Don't expect to find any answers there, except it seemed
to be conveying that it means different things to different people
Best answer may be (a more personal non-mechanical experience
with DFK LFK and BBBJ pretty much as standards.)
The degree of IOP and non-mechanical would be the big factors.
For rich dudes it would probably mean a more extended period of time,
dinner dates, vacation excursions together, etc. Something even
closer to but not quite in the Sugar Baby catagory