Totally agree the lines are blurred between the two, and you can get crash/rides cymbals. But I have a pasite 2002 17" crash which I also use as my ride in my really cut down, acoustic kit (snare, bass, hi-hats and ride).The main difference is SUPPOSED to be that a ride has a clearer "ping" or "click" sound and the wash doesn't build up as much when you ride it. The crash SHOULD open up more quickly than a ride when you play it near the edge. I've played countless rides and crashes that didn't live up to this clear defining line, and most of the time that's a good thing.
The technical difference that goes along with this description deals with the taper of a cymbal. A crash cymbal will be thicker near the bell and taper out to really thin near the edge. This allows it to "crash" easier--the wash and overtones are easier to draw out. A ride will be a more uniform thickness from near the bell to the edge.
Yes, you CAN put your high hat bottom cymbal up on a crash cymbal stand and use it as a crash or a ride, but would you really want to do that? It would most likely sound horrible. Lots of drummers use their cymbals for the purpose they're designated for (crash or ride), but if you like to use a cymbal for more than just one duty, then you should pick out cymbals that perform both functions in a way that meets your personal sonic criteria. Good luck with that!
Welcome to the forum!