The actual definition of an espadrille is described by Wikipedia as:
Espadrilles or alpargatas are normally casual, flat, but sometimes high-heeled shoes originating in the Pyrenees. They usually have a canvas or cotton fabric upper and a flexible sole made of jute rope. The jute rope sole is the defining characteristic of an espadrille; the uppers vary widely in style.
So, there you have it, the rope is the key. Personally, I usually gravitate to the more traditional style, either a neutral color or blue and white sailor stripes (for that joie de vivre!) But this year, the colors are so cute. I've included a red and a yellow, but I saw bold stripes and patterns as well. Some are flat, some are pointed, some are high, some are even suede, but all of them have the rope. And all are adorable!
This last one is truly the classic style. The ankle tie, the flat sole, and the stripes make for the perfect summer sandal (preferably worn on the Cote d'Azur).