A Leberknoedel is a Bavarian variety of the popular meatball, with liver added. Usually sold in soup tins. Inexpensive and very good. A "Knoedel" would be a dumpling, but Leberknoedel are more related to meatballs than to dumplings.
Semmelknoedel are a Bavarian speciality and consist of potatoes and/or breadcrumbs. They look and taste similar to dumplings. You also find them cut into stripes and fried in fat. Tip: The Pfanni company makes great instant Semmelknoedel. Check them out at any supermarket.