Traditionally, burnt ends are the overcooked (burnt) ends of the brisket that were chopped and served with sauce. Since we don't cook enough briskets to have enough true burnt ends, we usually make them from the brisket point.
Once a brisket is done I cut off the point, re-season it and put it back in the pit for a couple of hours to render more fat and give it a good bark. Then I cube the point and put it in a pan with sauce and cook it some more to set the sauce and get the outside of the chunks nice and crispy.