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 Nubuck:
This is a grain leather that has been slightly brushed on the surface to create a very fine velvet-like appearance. The texture of nubuck is finer than suede.
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.