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:
Slides are a sandal in which the upper does not extend to cover the heel of the foot. The wearer of Slides can simply slip on the shoe without having to tie, strap, or buckle it to secure.