Ginger is propagated by rhizomes, which are underground stems that grow horizontally and produce roots and shoots. Essentially, you can plant a piece of a ginger rhizome, and it will grow into a new plant. This is a common way to propagate ginger because it is easy and efficient, and it allows you to quickly produce many new plants from one parent plant. In simple terms, you can think of rhizomes as "cuttings" that you can take from an existing ginger plant and plant elsewhere to grow a new plant.