Flap meat is a great cut of beef. It is part of the belly, more specifically the inner oblique muscle, also known as top sirloin. It resembles flank steak (which also comes from the belly), but it’s slightly less fibrous and with a little more marbling.
Bark is the brown/black crust that forms on meat thanks to the Maillard effect among other things. Do not confuse bark with the charred surface you get on burnt meat, there is a night and day difference with both flavor and taste. The bark looks good and tastes great.