Along the sole from the toe box to the start of the heel cup is open space about 1 to 2 inches depends on size. Toe box and heel cup are seperate from each other. The most sexy of pumps. Usually patent leather. They are usually flat heels, but can be high-heeled as well.
Some people refer to any shoe with ankle straps as a sandel.
These are locked together, preventing the wearer from removing the shoes without the key to the lock. Sometimes a shoe or boot is equipped with locking ankle straps per design, serving the same function. Like mules but mostly made of wood, - a sort of high heeled clog. A kind of mules, but with closed toe box. Also note that high heeled shoes tend to feel smaller than flats.