Originally Posted by vince

A flip-flop is thong, but a thong isn't always a flip-flop. Flip-flops are the rubber/plastic cheap ones. Therefore it's ok to call them thongs. Other thongs can be leather and/or have other design characterics. All thongs have the piece between toes. Some thongs have a strap that goes over the big toe.

Sandals have the horizontal bands going across the foot with possibly a heel strap added.