"Hamburger onions" typically refers to the way the onions are prepared for a hamburger. These onions can be raw or cooked depending on personal preference. Raw onions provide a pungent, sharp flavor and a crunchy texture, often red or white onions are used in this way. Cooked onions, on the other hand, are usually sautéed or caramelized to bring out a sweet, savory flavor. Yellow or sweet onions are often chosen for this preparation. The term "hamburger onions" doesn't denote a specific type of onion, but rather describes their usage in the context of a hamburger.