While people often think of and refer to it as a root, ginger is technically a vegetable. It's the rhizome of the Zingiber officinale plant. A rhizome is a type of bulbous stem that grows horizontally underground and stores starches and other nutrients necessary for the survival of the parent plant. Zingiber officinale rhizomes also hold large quantities of a botanical compound called "gingerols," which gives ginger bulbs the zesty, piquant flavor for which they're known.