Heel-to-Toe drop is the difference between the thickness of a shoe’s sole at the heel and the thickness at the toe. Most modern shoes add thick cushioning under the heels of shoes, which encourages people to strike the ground with their heels first when running. This creates a harsher, more jarring impact than striking midfoot or forefoot first—the way people run when barefoot.
Note: it is normal to walk in minimal shoes differently than the way you run. See this blog post for more details.