What is Heel of Round?
The Beef Heel of Round represents a cut from the beef round immediately above the hock. This roast is composed of many small muscle groups, has a lot of seam fat, and is one of the least tender cuts of beef.

Braising for long periods of time works best for that cut.

Bottom round is rump roast and the top part furthest away from the hock.

Source: https://animalscience.unl.edu/beef-meat-identification