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 Slippers:
A type of shoe typically designed for indoor use that can be a variety of styles, including slides, mocassins, scuffs, booties, thongs, or loafers. Usually the uppers are made of soft leather or other fabrics (as opposed to tougher fabrics like hard leather that regular shoes are made of) and are sometimes lined with soft materials like felt, shearling or wool.