Flat Shoes are shoes in a wide variety of different types of styles that they have no heel serving to add height/elevation to the wearer. Flat shoes may have a very small heel height; however, generally this will be 1/2" or less.
About Heel:
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).