In America, rump is commonly known as the round. It is a muscular cut of beef that comes from the rear of the cow. It's a relatively lean cut and can be tougher than other cuts, but can still be tender if it's cooked correctly.
In the UK, rump is a popular cut of beef and is often used for roasting or grilling. In South America, the rump cap is called Picanha and is a popular cut of beef in Brazil. It is typically grilled and seasoned with coarse salt.