Heel-to-toe drop, simply drop, differential, they’re all ways to call the difference in height in millimetres between the heel of the shoe and the toe.
Traditional running shoes have a drop of 10-12 millimetres, low-drop shoes usually 4-6 millimetres, and there is a whole category of zero-drop shoes.
A higher drop favours landing with the heel, while lower drops move the gait to a midfoot or forefoot landing. It’s personal preference, although we do recommend the traditional drop for beginners, as low-drop shoes might place excessive stress on your calf muscles.