The purist, jazz drummer in me will tell you there is no difference. You can place a cymbal wherever you want and play it however you want regardless of what word the manufacturer decided to print on it. You can ride a crash and crash a ride. "Crash" and "ride" are just divisions we've made based on how well they produce certain kinds of sounds. So really the only distinctions you can make are based on sound. Do you like the way it sounds when you crash it? Then crash it. Do you like the way it sounds when you ride it? Then ride it. But crash and ride don't have to be different cymbals - just different play styles. I often run an 18" "crash/ride" on the left and a thicker 20" "ride" on the left but I crash and ride both of them interchangeably depending on the music. So which one is my ride cymbal? Both. Which is my crash cymbal? Both. They just crash and ride in different ways and at different intensities. I also have a 17" "dark crash" that I like to ride in smaller venues and stuff. It's small and light and opens up at a pretty low volume. So it works pretty well in small, intimate spaces and playing lightly with light sticks. Alternatively, it makes an excellent crash cymbal in sort-of medium-loud live music or in the studio where volume doesn't really matter so much. So I feel it has pretty diverse applications.
Idk, that's a pretty philosophical approach to a simple question, but I legitimately feel the boxes we place on ourselves - you can only crash and crash and ride a ride - are limiting and inhibit our creativity and musicality. So go, crash your rides and ride your crashes. Experiment. Find what sounds good and let that be the ultimate measure of what a cymbal is. Size, thickness, position, even the label on the cymbal - no one in the audience or listening to your record is going to know or care about these trivialities - only sound matters.