They're exactly the same and completely different.

Asking the difference between a rump roast and a pot roast is like asking the difference between a ribeye and a steak: there is no difference, but there's also all the difference in the world. "Pot roasts" (and "steaks") are names for ways a cut of meat is prepared, while a rump roast (or a ribeye) is a specific cut of meat from a specific part of the animal. If this question of difference between a rump roast and a pot roast isn't a direct comparison, then why ask it? Because it brings up one very important piece of culinary information: not all cuts of meat can be prepared in the same way.

Pot Roast with Vegetables
Credit: LauriPatterson/Getty Images

A pot roast is a meat that is typically slowly braised (cooked in a liquid) at a low temperature for a long period of time—like in a Crock Pot. This method of cooking does something very different to the meat from other methods of cooking that apply high heat for a shorter period of time, and each method should be used for the cut of meat best suited for its time and heat. Generally speaking, the muscles a cow uses least often, like the ribeye (located in the upper part of the rib cage), are exceptionally tender cuts of meat as is and should be cooked quickly. These fatty cuts of meat contain very little tough connective tissue because they are not worked frequently by the animal. The rump roast, however, sits at the juncture of the cow's leg quarters and the rest of its body. This cut of meat is very tough, packed with collagen and dense muscles fibers, and has less fat because it's constantly used by the cow to walk and support its own weight.

Tough cuts of meat like the rump roast require low heat for a long period of time (in contrast to the quick-cooking high heat of a ribeye steak). The long cook time allows the tough connective tissue to break down, and it allows the firm collagen to liquify into gelatin that makes for a juicy and succulent pot roast. If cooked quickly, a rump roast would be as tough as a shoe, but slowly braised as a pot roast, a rump roast melts in your mouth with complex flavorful juices that are only released by the meat over a long period of cooking.