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 Slides:
A backless, open-toed shoe that is generally a type of sandal. Slides can be high heeled, flat heeled, or somewhere inbetween; may cover nearly the entire foot from ankle to toe; or may have only one or two narrow straps.