I was trying to explain this to a friend on mine yesterday while shopping for new cologne, and leather flip flops.
So here they are....
Potential potential: Someone you have taken note of, and realize there could be some potential; but you don't really know them well enough yet to be sure. Further investigation is necessary.
Squish: Someone you have seen in multiple social situations. Conversation is easy and you find them attractive. You get excited when you know you will be seeing them; but you don't touch up your makeup before hand. If they asked you out you would be excited; but you would also be fine making them your new best friend.
Crush: If you know you will be seeing them you take extra care to pick out your outfit. You go out of your way to catch his eye across the room. You have weighed your chances with all your friends and they have given you the green light. You make sure you wear the perfume he casually mentioned liking. His name has appeared in your journal.
Crushing Crush: He is the ONLY thing you think about. When you talk to him you laugh too loud. You buy new clothes you think it will impress him. There are hearts around his name in your journal. You panic when he doesn't text you back right away. You know all of his "stats" and the name of the puppy he had growing up. You drive by his place on the way home. When he asks your friend out you are barely functional the next day.
I try to make sure I never pass the "Squish zone." Anything else gets real messy and hearts get broken and friendships destroyed. No one wins once the crush develops.