Yes, ginger is a stem, specifically an underground stem called a rhizome. It's not a root, although it's often referred to as "ginger root." A rhizome is a modified stem that grows horizontally underground, often with nodes and internodes, which are characteristics of stems. The parts of the ginger plant that we use as a spice and for medicinal purposes are the rhizomes.
Examples of other rhizomes:
- Turmeric
- Bamboo
- Iris