https://www.biologyonline.com/dictionary/rhizome
Rhizomes are stems positioned either horizontally or vertically under the ground with roots or shoots coming out from the nodes and surrounded by leaves (either scale-like, green leaves, or buds). They are stems and not roots because they have the fundamental features of a stem, such as the presence of internodes, small leaves, buds, and nodes. They are, however, modified stems. By modified, it means that they are specialized for functions other than providing mechanical support. Rhizomes, in particular, are specialized for storing food. Thus, some of the rhizomes are cultivated to be harvested and used as sources of food for humans, e.g. turmeric and ginger.