Top round one of the major subprimals of the beef round primal cut.
Beef round is a large primal cut consisting of well-exercised muscles from the leg and rump of the animal. But the top round (also called inside round, because it comes from the inside of the leg), is actually a good cut of meat for roasting, as long as it's done slowly at a low temperature.
Cooking it this way ensures that it comes out medium rare, thus preserving what little tenderness the top round has to begin with. It's also important to slice it thinly. Roasted top round is ideal for making roast beef for sandwiches.
Top round can also be fabricated into steaks, usually referred to as top round steaks. I'd be less inclined to cook a top round steak over the grill, simply because there are so many better options.
Having said that, if I were stuck on an island with nothing but a thick slab of top round and a grill, I'd marinate it, grill it quickly over high heat and then slice it thinly against the grain. This particular preparation happens to be known as London broil, and if I served it to the natives, I suspect they'd be friendly—provided I sliced it thinly enough. Otherwise, all that chewing would undoubtedly make them restless.
Top Round on the Grill or Smoker
You can cook a top round roast on the grill, and it's surprisingly good. Surprisingly because you might associate the grill with high-heat cooking, and we just got done saying that top round works best with roasted slowly.
And that's true. So the key with grilling top round is to use indirect heat. What that means is building a two-zone fire in your grill. If you're cooking on a gas grill, that's easy. Just heat up one of the burners and cook the roast on the side away from the burner, with the lid closed. But with a charcoal grill you'll want to pile your coals on one side and cook the roast on the other side (again, with the lid on).
You're going to want to keep the temperature of the grill to around 300 F. Again, this is easier using a gas grill, but with a charcoal grill, the air vents and a dome thermometer are your friend. A 3-pound top round should turn out medium rare in an hour or two, but a probe thermometer will take the guesswork out. Just set it to 125 F and take it off the grill when it beeps, then let it rest for 30 minutes while the temperature continues to climb to its eventual 135 F.
If you're smoking your top round, your smoker needs to be at 225 to 250 F. At that temperature, the same 3-pound roast will take two to three hours to reach medium rare. And again, don't forget to rest the meat.