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 Mary Janes:
A girl's or woman's shoe that is styled after shoes that were traditionally worn by children. Mary janes can have varying heel heights and come in a variety of styles. Signature features of a mary jane include (i) a strap (or many straps) that cross over the top of the foot and (ii) a short, rounded toe box. Mary janes traditionally had low or flat heels. However, mary janes now come in a variety of heel heights.