Beef ribs are cut right off the rib roast. They are comparable to pork baby back ribs but they are more tough and not as much meat. This isn't necessarily a bad thing, because when they are cooked properly, slow cooked/braised, they are amazingly tender and full of flavor!
One slab typically has 7-8 ribs and serves 2 - 3 people. A half slab runs 1.5 - 2 lbs and a full slab runs 3- 4 lb.