A heel is the bottom, back part of a shoe or boot that provides elevation. The styling and construction of a heel may vary (i.e., stacked, stilletto, spiked, sculptured, kitten).
About Sandals:
Sandals are footwear made of a sole that is held to the foot utilizing straps or thongs. Sandals are characterized by exposing the foot.
About Slingbacks:
Slingbacks are a type in shoe in which the heel is exposed yet is contained or secured by a strap that sits above the heel around the ankle.